fix(qqbot): unlink temp wav on STT failure path

[Zhekinmaksim]

_stt_voice_attachment writes the downloaded voice payload to a NamedTemporaryFile(delete=False) and then calls the configured self-hosted STT endpoint. Previously the temp WAV was unlinked only after _call_stt returned - if it raised httpx.HTTPStatusError, httpx.TransportError, or IOError, the outer except swallowed the error but left the file behind. In a long-running bot, transient STT outages turn into a steady leak of one WAV per failed transcription in $TMPDIR.

Wrap _call_stt in try/finally so wav_path is always unlinked, matching the silk_path cleanup pattern already used a few lines below in _convert_audio_to_wav_file.

Test plan

Added two regression tests in TestVoiceAttachmentTempCleanup:

• test_temp_wav_cleaned_up_on_stt_failure - asserts the temp file no longer exists after _call_stt raises httpx.HTTPStatusError. Fails on current main, passes with this patch.
• test_temp_wav_cleaned_up_on_stt_success - sanity check that the happy path still cleans up.

Full tests/gateway/test_qqbot.py: 144 passed, 2 unrelated failures (test_connect_uses_redirect_guard_hook, test_open_ws_honors_proxy_env) that fail on unmodified main as well due to local httpx mock setup.

[Zhekinmaksim]

Quick bump on this PR. The cleanup is still current from my side and should be ready for review if it is still relevant.

[Zhekinmaksim]

Following up on this one as well. The PR is still technically clean from my side: all recorded CI checks on the branch are green, it is still mergeable, and I do not see any review comments or requested changes attached to it. If the fix is still relevant, this looks like it only needs maintainer review/decision rather than more code work from me.

[Zhekinmaksim]

Hi, gentle follow-up on this PR. The cleanup is still current from my side, and I would appreciate a review when convenient if it is still relevant.

[teknium1]

Merged into main via consolidated salvage PR #73515 (merge c911a5f10f). Your QQ temp-WAV cleanup fix (always unlink, not just on the happy path) was cherry-picked with your authorship.

Your contribution is credited to you in git history. Thank you! Closing this PR as merged-via-salvage.