Python: Fix responses execute tool call type error

[Sushmithamallesh]

Note

Narrow execute_tool_call to only handle ResponseFunctionToolCall and simplify logic by removing ChatCompletionMessageToolCall support.

• OpenAI Responses provider (python/composio/core/provider/_openai_responses.py):
  • Narrow execute_tool_call to accept only ResponseFunctionToolCall and simplify slug/argument parsing.
  • Remove ChatCompletionMessageToolCall import and related branching logic.

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