Add missing Python function docstrings (#13105)

* Add missing Python function docstrings

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Co-authored-by: UltralyticsAssistant <web@ultralytics.com>
Co-authored-by: Ultralytics Assistant <135830346+UltralyticsAssistant@users.noreply.github.com>

utils/loggers/__init__.py

@@ -23,6 +23,7 @@ try:
 except ImportError:
 
     def SummaryWriter(*args):
+        """Fall back to SummaryWriter returning None if TensorBoard is not installed."""
         return None  # None = SummaryWriter(str)