Refactor and modernize namespace declarations

 * Completely remove inline namespace v2
 * Flatten some unnecessarily deep namespace nesting
 * Move DummyClientFace, Segmenter, SegmentFetcher to namespace ndn
 * Move all unit tests to namespace ndn::tests

Change-Id: I8bcfcf9fd669936a3277d2d5d505f765b4b05742
diff --git a/tests/unit/net/dns.t.cpp b/tests/unit/net/dns.t.cpp
index b6a24b5..ac734dd 100644
--- a/tests/unit/net/dns.t.cpp
+++ b/tests/unit/net/dns.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2022 Regents of the University of California.
+ * Copyright (c) 2013-2023 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -26,10 +26,9 @@
 
 #include <boost/asio/io_service.hpp>
 
-namespace ndn {
-namespace dns {
-namespace tests {
+namespace ndn::tests {
 
+using namespace ndn::dns;
 using boost::asio::ip::address_v4;
 using boost::asio::ip::address_v6;
 
@@ -169,6 +168,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestDns
 BOOST_AUTO_TEST_SUITE_END() // Net
 
-} // namespace tests
-} // namespace dns
-} // namespace ndn
+} // namespace ndn::tests
diff --git a/tests/unit/net/ethernet.t.cpp b/tests/unit/net/ethernet.t.cpp
index 162170b..0fc5357 100644
--- a/tests/unit/net/ethernet.t.cpp
+++ b/tests/unit/net/ethernet.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2018 Regents of the University of California,
+ * Copyright (c) 2014-2023 Regents of the University of California,
  *                         Arizona Board of Regents,
  *                         Colorado State University,
  *                         University Pierre & Marie Curie, Sorbonne University,
@@ -29,8 +29,7 @@
 
 #include "tests/boost-test.hpp"
 
-namespace ndn {
-namespace tests {
+namespace ndn::tests {
 
 BOOST_AUTO_TEST_SUITE(Net)
 BOOST_AUTO_TEST_SUITE(TestEthernet)
@@ -113,5 +112,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestEthernet
 BOOST_AUTO_TEST_SUITE_END() // Net
 
-} // namespace tests
-} // namespace ndn
+} // namespace ndn::tests
diff --git a/tests/unit/net/face-uri.t.cpp b/tests/unit/net/face-uri.t.cpp
index d21d70f..34e050e 100644
--- a/tests/unit/net/face-uri.t.cpp
+++ b/tests/unit/net/face-uri.t.cpp
@@ -34,8 +34,7 @@
 
 #include <boost/concept_check.hpp>
 
-namespace ndn {
-namespace tests {
+namespace ndn::tests {
 
 BOOST_CONCEPT_ASSERT((boost::EqualityComparable<FaceUri>));
 
@@ -614,5 +613,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestFaceUri
 BOOST_AUTO_TEST_SUITE_END() // Net
 
-} // namespace tests
-} // namespace ndn
+} // namespace ndn::tests
diff --git a/tests/unit/net/network-configuration-detector.cpp b/tests/unit/net/network-configuration-detector.cpp
index 84e1244..f8a8816 100644
--- a/tests/unit/net/network-configuration-detector.cpp
+++ b/tests/unit/net/network-configuration-detector.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2018 Regents of the University of California.
+ * Copyright (c) 2013-2023 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -27,35 +27,30 @@
 #include <boost/asio/ip/udp.hpp>
 #include <boost/range/iterator_range_core.hpp>
 
-namespace ndn {
-namespace tests {
-
-bool NetworkConfigurationDetector::m_isInitialized = false;
-bool NetworkConfigurationDetector::m_hasIpv4 = false;
-bool NetworkConfigurationDetector::m_hasIpv6 = false;
+namespace ndn::tests {
 
 bool
 NetworkConfigurationDetector::hasIpv4()
 {
-  if (!m_isInitialized) {
+  if (!s_isInitialized) {
     detect();
   }
-  return m_hasIpv4;
+  return s_hasIpv4;
 }
 
 bool
 NetworkConfigurationDetector::hasIpv6()
 {
-  if (!m_isInitialized) {
+  if (!s_isInitialized) {
     detect();
   }
-  return m_hasIpv6;
+  return s_hasIpv6;
 }
 
 void
 NetworkConfigurationDetector::detect()
 {
-  typedef boost::asio::ip::basic_resolver<boost::asio::ip::udp> BoostResolver;
+  using BoostResolver = boost::asio::ip::basic_resolver<boost::asio::ip::udp>;
 
   boost::asio::io_service ioService;
   BoostResolver resolver(ioService);
@@ -66,22 +61,21 @@
   boost::system::error_code errorCode;
   BoostResolver::iterator begin = resolver.resolve(query, errorCode);
   if (errorCode) {
-    m_isInitialized = true;
+    s_isInitialized = true;
     return;
   }
   BoostResolver::iterator end;
 
   for (const auto& i : boost::make_iterator_range(begin, end)) {
     if (i.endpoint().address().is_v4()) {
-      m_hasIpv4 = true;
+      s_hasIpv4 = true;
     }
     else if (i.endpoint().address().is_v6()) {
-      m_hasIpv6 = true;
+      s_hasIpv6 = true;
     }
   }
 
-  m_isInitialized = true;
+  s_isInitialized = true;
 }
 
-} // namespace tests
-} // namespace ndn
+} // namespace ndn::tests
diff --git a/tests/unit/net/network-configuration-detector.hpp b/tests/unit/net/network-configuration-detector.hpp
index 5c0c34b..7264e68 100644
--- a/tests/unit/net/network-configuration-detector.hpp
+++ b/tests/unit/net/network-configuration-detector.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2021 Regents of the University of California.
+ * Copyright (c) 2013-2023 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -47,8 +47,7 @@
     } \
   } while (false)
 
-namespace ndn {
-namespace tests {
+namespace ndn::tests {
 
 class NetworkConfigurationDetector
 {
@@ -64,12 +63,11 @@
   detect();
 
 private:
-  static bool m_isInitialized;
-  static bool m_hasIpv4;
-  static bool m_hasIpv6;
+  static inline bool s_isInitialized = false;
+  static inline bool s_hasIpv4 = false;
+  static inline bool s_hasIpv6 = false;
 };
 
-} // namespace tests
-} // namespace ndn
+} // namespace ndn::tests
 
 #endif // NDN_CXX_TESTS_UNIT_NET_NETWORK_CONFIGURATION_DETECTOR_HPP
diff --git a/tests/unit/net/network-monitor-stub.t.cpp b/tests/unit/net/network-monitor-stub.t.cpp
index 453a510..0ef8a9d 100644
--- a/tests/unit/net/network-monitor-stub.t.cpp
+++ b/tests/unit/net/network-monitor-stub.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2018 Regents of the University of California.
+ * Copyright (c) 2013-2023 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -23,9 +23,9 @@
 
 #include "tests/boost-test.hpp"
 
-namespace ndn {
-namespace net {
-namespace tests {
+namespace ndn::tests {
+
+using namespace ndn::net;
 
 BOOST_AUTO_TEST_SUITE(Net)
 BOOST_AUTO_TEST_SUITE(TestNetworkMonitorStub)
@@ -120,6 +120,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestNetworkMonitorStub
 BOOST_AUTO_TEST_SUITE_END() // Net
 
-} // namespace tests
-} // namespace net
-} // namespace ndn
+} // namespace ndn::tests
diff --git a/tests/unit/net/network-monitor.t.cpp b/tests/unit/net/network-monitor.t.cpp
index 132d0db..4515258 100644
--- a/tests/unit/net/network-monitor.t.cpp
+++ b/tests/unit/net/network-monitor.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2018 Regents of the University of California.
+ * Copyright (c) 2013-2023 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -25,9 +25,9 @@
 
 #include <boost/asio/io_service.hpp>
 
-namespace ndn {
-namespace net {
-namespace tests {
+namespace ndn::tests {
+
+using namespace ndn::net;
 
 BOOST_AUTO_TEST_SUITE(Net)
 BOOST_AUTO_TEST_SUITE(TestNetworkMonitor)
@@ -69,6 +69,4 @@
 BOOST_AUTO_TEST_SUITE_END() // TestNetworkMonitor
 BOOST_AUTO_TEST_SUITE_END() // Net
 
-} // namespace tests
-} // namespace net
-} // namespace ndn
+} // namespace ndn::tests