[core] Adjust message when there is no class in the module

Warning only on a module/file without any element in it.
Use Debug level for package/folder, so it does not generate messages by
default.

Provide full-path to ease debugging.

Author: fabiencastan

meshroom/core/__init__.py

@@ -100,7 +100,11 @@ def loadClasses(folder: str, packageName: str, classType: type) -> list[type]:
                            and issubclass(plugin, classType)]
 
                 if not plugins:
-                    logging.warning(f"No class defined in plugin: {pluginModuleName}")
+                    # Only packages/folders have __path__, single module/file do not have it.
+                    isPackage = hasattr(pluginMod, "__path__")
+                    # Sub-folders/Packages should not raise a warning, so we adjust the verbosity level.
+                    verbosity = logging.DEBUG if isPackage else logging.WARNING
+                    logging.log(verbosity, f"No class defined in plugin: {package.__name__}.{pluginName} ('{pluginMod.__file__}')")
 
                 for p in plugins:
                     p.packageName = packageName