fix: mcp chinese args (#359)

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit

* **Bug Fixes**
* Fixed encoding/decoding of proxy arguments in MCP proxy forwarding to
properly handle special and non-ASCII characters.

* **Tests**
* Updated test cases to verify correct handling of non-ASCII characters
in tool invocations.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: akitaSummer