Applied google-readability-namespace-comments clang-tidy fixes

src/util/error.h

@@ -34,4 +34,4 @@ struct substring_delimiter_not_found : public virtual std::runtime_error {
     {
     }
 };
-}
+} // namespace clanguml::error

src/util/thread_pool_executor.cc

@@ -90,4 +90,4 @@ std::packaged_task<void()> thread_pool_executor::get()
     return res;
 }
 
-}  // namespace clanguml::util
+} // namespace clanguml::util