Make patch_aiobotocore fixture reversible to prevent state leakage

[Copilot]

The patch_aiobotocore session-scoped fixture mutated global state (aiobotocore.endpoint.convert_to_response_dict and aiobotocore.httpchecksum.AioAwsChunkedWrapper attributes) without cleanup, violating fixture teardown best practices.

Changes:

• Save original function and attributes before mutation
• Convert fixture to yield-based pattern with teardown
• Restore original state at session end

@fixture(scope="session", autouse=True)
def patch_aiobotocore():
    # ... setup code ...
    
    # Save originals
    original_convert_to_response_dict = aiobotocore.endpoint.convert_to_response_dict
    saved_attrs = {}
    for attr in ("_make_chunk", "read"):
        if hasattr(aiobotocore.httpchecksum.AioAwsChunkedWrapper, attr):
            saved_attrs[attr] = getattr(aiobotocore.httpchecksum.AioAwsChunkedWrapper, attr)
            delattr(aiobotocore.httpchecksum.AioAwsChunkedWrapper, attr)
    
    yield
    
    # Restore in teardown
    aiobotocore.endpoint.convert_to_response_dict = original_convert_to_response_dict
    for attr, value in saved_attrs.items():
        setattr(aiobotocore.httpchecksum.AioAwsChunkedWrapper, attr, value)

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