feat(tts): add language to vendor metadata

[wangyimin-agora]

What changed

• Add language to Rime and OpenAI TTS vendor metadata.
• Update TTS Guarder metadata checks to accept expected metadata as a subset.
• Validate connection status vendor data through vendor_info.vendor.
• Allow non-audio events after tts_flush_end while continuing to reject audio frames.

Why

Adding language made exact metadata comparisons fail even though the required metadata remained correct. The connection-status test also expected an outdated top-level vendor field, and the flush test treated valid non-audio events as extra output.

Validation

• Rime focused Guarder: test_flush and test_connection_status passed (2 passed).
• Rime full Guarder after the metadata subset fix: 13 passed, 1 skipped, with the unrelated empty-text latency case still failing its 500 ms threshold.
• OpenAI connection-status case skipped as expected because OpenAI TTS is HTTP-based and the case covers WebSocket TTS extensions.
• OpenAI vendor metadata tests passed (4 passed).
• Ran git diff --check.

[wangyimin-agora]

Closing this fork-based PR; it will be replaced by a PR from the upstream dev/tts_language branch.