fix: correct log_level type annotation in add_logging_middleware

[mazyu36]

Summary

Fix type annotation mismatch in add_logging_middleware function.

The log_level parameter was incorrectly annotated as int but actually receives string values ('DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL') from argparse.

Changes

Changed log_level parameter type annotation from int to str in add_logging_middleware() function in mcp_proxy_for_aws/server.py

User experience

No user-facing changes.

Checklist

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• I have reviewed the contributing guidelines
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• Changes have been tested
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Is this a breaking change? (Y/N)

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• No

Please add details about how this change was tested.

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