test: use official MCP SDK in Python tests
- Add mcp>=1.0.0 and pytest-asyncio to test requirements
- Update TestMcpJsonRpcProtocol to use MCP SDK's ClientSession
- Update TestMcpEnvVarFiltering to use MCP SDK
- Keep raw websocket tests for edge cases (TestMcpJsonRpcProtocolRaw)
- Configure pytest-asyncio in pytest.ini
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
