feat(python): add MCP extension and tool adapter

[SaladDay]

Summary

• add MCP connection/session manager with stdio & SSE configs for namespaced tool discovery
• wrap MCP tools in a google-adk BaseTool bridge and normalize structured results
• document usage, extend feature matrix, add unit coverage

Test

cd ali-agentic-adk-python && pytest tests/test_mcp_extension.py

[SaladDay]

@pawpawya ptal, thanks😄

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✅ SaladDay
❌ xiaoxuan-lp
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