Add caughtstealingpercentage to docstring documentation

Updates the SimplePitchingSplit class docstring to include documentation
for the caughtstealingpercentage field that was added in the previous commit.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: coreylane

mlbstatsapi/models/stats/pitching.py

@@ -152,6 +152,8 @@ class SimplePitchingSplit:
         The number of inherited runners for the pitcher.
     age : int
         The age of the pitcher.
+    caughtstealingpercentage : str
+        The caught stealing percentage for the pitcher.
     """
     summary: Optional[str] = None
     gamesplayed: Optional[int] = None