perf: add py-libp2p v0.6 implementation

[acul71]

Summary

Add a py-libp2p perf implementation under perf/impl/py-libp2p/v0.6/ so the test-plans perf runner can benchmark Python alongside Go, JS, Rust, etc.

Scope

• CLI aligned with existing perf binaries (--run-server, --server-address, --transport, --upload-bytes, --download-bytes; JSON on stdout, logs on stderr).
• Makefile builds/runs via pinned py-libp2p + venv (see impl README).
• Wire py-libp2p in perf/impl/Makefile, runner/versionsInput.json, runner/src/versions.ts, and runner/src/index.ts test-filter allow-list.
• Top-level perf/README.md updates as needed.

Notes

• TCP and QUIC transport stacks per versionsInput.json / runner config.
• QUIC may need harness-level workarounds until py-libp2p core catches up; documented in impl README where relevant.

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PR will reference this issue.