fix(sound): guard recording lifecycle

[martin-henz]

Re-opens #839, which was automatically closed (not merged) when its base branch conductor-migration was deleted after being merged into master via #680. This branch cherry-picks the original commits from @11suixing11 unchanged, onto current master.

Summary

• reserve one in-flight recording slot synchronously when record or record_for accepts a request
• make record's returned stop function idempotent so repeated calls reuse one stopRecording() promise
• release recording state after successful completion and after startRecording/stopRecording failures
• guard cleanup with a per-recording generation token so a stale stop() cannot release a newer reservation

Fixes #799

Why

record and record_for schedule delayed work before io().startRecording() runs. The existing activePlayCount check prevents recording during playback, but there was no state reserved for a recording request itself. Two quick calls could therefore schedule independent timeout chains and eventually attempt overlapping recordings against the same tab-side recorder.

The PR reserves recording state at call time, so a second request fails before either timeout chain reaches startRecording().

Review Follow-up

CodeRabbit flagged a stale cleanup edge case: after startRecording() rejects and releases the reservation, invoking the old returned stop() could settle a second cleanup after a newer recording had reserved the mic.

reserveRecording() now returns a generation token, and releaseRecording() only clears state when that token still identifies the active reservation. The regression test covers this exact sequence:

1. the first record() fails during startup
2. a newer recording reserves the mic
3. the stale stop() from the failed first recording is invoked
4. the newer reservation remains active

Testing (from original PR, re-verify on CI)

• yarn workspace @sourceacademy/bundle-sound test (71 passed)
• yarn workspace @sourceacademy/bundle-sound tsc
• yarn workspace @sourceacademy/bundle-sound lint

Original author: @11suixing11

[gemini-code-assist]

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