Adds __str__ method for TextWithMetadata (jupyterlab#250)

* Adds __str__ method for TextWithMetadata

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

packages/jupyter-ai-magics/jupyter_ai_magics/magics.py

@@ -49,6 +49,9 @@ def __init__(self, text, metadata):
         self.text = text
         self.metadata = metadata
 
+    def __str__(self):
+        return self.text
+
     def _repr_mimebundle_(self, include=None, exclude=None):
         return ({"text/plain": self.text}, self.metadata)