Use nested namespace

It's a mechanical change to modernize the code base

src/tools/components.cpp

@@ -25,9 +25,7 @@
 #include <string>
 #include <vector>
 
-namespace osrm
-{
-namespace tools
+namespace osrm::tools
 {
 
 using TarjanGraph = util::StaticGraph<void>;
@@ -103,7 +101,6 @@ struct FeatureWriter
 };
 
 //
-} // namespace tools
 } // namespace osrm
 
 int main(int argc, char *argv[])