fix: convert mislabeled audio before STT

[zzz27578]

Summary

• verify audio magic bytes before skipping same-extension conversion
• convert non-WAV payloads that were materialized with a .wav suffix
• preserve the existing Ogg/Opus no-op behavior
• add regression coverage for AMR bytes stored under a .wav filename

Root cause

MediaResolver can materialize extensionless or base64 audio with the default .wav suffix. ensure_wav() correctly detects that the bytes are not WAV and requests WAV conversion, but convert_audio_format() previously returned early based only on the filename suffix. The unchanged non-RIFF payload was then rejected by the MiMo STT boundary validation.

This change keeps the fast path only when both the suffix and detected audio format match the requested output format.

Follow-up to #9113 and #9118.

Validation

• uv run pytest tests/test_media_utils.py -q -k "not test_file_uri_to_path_supports_localhost_and_encoded_paths" ? 50 passed, 1 Windows-specific path test deselected
• uv run pytest tests/test_mimo_api_sources.py -q ? 19 passed
• uv run ruff check astrbot/core/utils/media_utils.py tests/test_media_utils.py
• uv run ruff format --check astrbot/core/utils/media_utils.py tests/test_media_utils.py
• manual Windows verification with aiocqhttp + MiMo STT: a QQ voice message was converted, transcribed correctly, and produced the expected 111 response

Summary by Sourcery

Ensure audio format conversion validates the underlying magic bytes instead of relying solely on file extensions before speech-to-text processing.

Bug Fixes:

• Fix WAV conversion for non-WAV audio payloads that were materialized with a .wav suffix to avoid STT boundary rejection.

Tests:

• Add regression test verifying ensure_wav converts non-WAV AMR bytes stored under a .wav filename and produces a valid RIFF/WAV output.

[sourcery-ai]

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[gemini-code-assist]

Code Review

This pull request enhances the convert_audio_format function in astrbot/core/utils/media_utils.py to verify the actual audio format using _get_audio_magic_type rather than relying solely on the file extension, and adds a corresponding unit test. The reviewer correctly identified that calling _get_audio_magic_type synchronously inside an asynchronous function will block the asyncio event loop, and suggested offloading this operation to a separate thread using asyncio.to_thread.

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