chore: get rid of cmdstats_map (#1687)

cmdstats_map were on the hotpath and are needed only to update the command stats.
Instead, I introduced the stats withing the CommandId itself that we lookup anyways.
Also, it removes fragile dependency on naked command name char* pointers.

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

src/server/main_service.h

@@ -68,6 +68,10 @@ class Service : public facade::ServiceInterface {
     return registry_.Find(cmd);
   }
 
+  CommandRegistry* mutable_registry() {
+    return &registry_;
+  }
+
   facade::ErrorReply ReportUnknownCmd(std::string_view cmd_name);
 
   // Returns: the new state.