Use nested namespace

It's a mechanical change to modernize the code base

unit_tests/contractor/contracted_edge_container.cpp

@@ -7,9 +7,7 @@
 using namespace osrm;
 using namespace osrm::contractor;
 
-namespace osrm
-{
-namespace contractor
+namespace osrm::contractor
 {
 
 bool operator!=(const QueryEdge &lhs, const QueryEdge &rhs) { return !(lhs == rhs); }
@@ -27,7 +25,6 @@ std::ostream &operator<<(std::ostream &out, const QueryEdge &edge)
     out << "{" << edge.source << ", " << edge.target << ", " << edge.data << "}";
     return out;
 }
-} // namespace contractor
 } // namespace osrm
 
 BOOST_AUTO_TEST_SUITE(contracted_edge_container)

unit_tests/contractor/helper.hpp

@@ -3,9 +3,7 @@
 
 #include "contractor/contractor_graph.hpp"
 
-namespace osrm
-{
-namespace unit_test
+namespace osrm::unit_test
 {
 
 using TestEdge = std::tuple<unsigned, unsigned, int>;
@@ -38,7 +36,6 @@ inline contractor::ContractorGraph makeGraph(const std::vector<TestEdge> &edges)
 
     return contractor::ContractorGraph{max_id + 1, input_edges};
 }
-} // namespace unit_test
 } // namespace osrm
 
 #endif