Nest namespaces explicitly instead of c++17 shortcut

include/common_bench/plot.h

@@ -9,7 +9,8 @@
 #include <fmt/core.h>
 #include <vector>
 
-namespace common_bench::plot {
+namespace common_bench {
+namespace plot {
 
 const int kArgonneBlue = TColor::GetColor(0x1f, 0x77, 0xb4); // not really
 
@@ -41,4 +42,6 @@ void draw_label(int ebeam, int pbeam, const std::string_view detector) {
 
 } // namespace common_bench::plot
 
+} // namespace common_bench
+
 #endif