Keep a stop from cutting off playback that already restarted (#6082)

# What does this implement/fix?

Stopping a queue cleared every audio buffer on it, without checking
which playback session
those buffers belonged to. The rest of the stop already checks: the
session itself and the
audio processing are only released when the session that was stopped is
still the current
one. The buffer cleanup was not.

So when playback restarts before a stop finishes, the new session
survives the stop but its
audio does not, and the track that just started loses the audio it was
filling. That needs
the playback lock to give up on a wedged holder first, so it takes a
stop that hangs for
thirty seconds on an unresponsive speaker.

Every audio buffer now records the session that asked for it, and a stop
releases only its
own. A buffer with no session recorded is still released, because a stop
must never leave a
producer running.

Follow-up to a review comment on #6077, which deliberately left this out
of scope.

- Audio buffers are claimed by the playback session that asks for them,
recorded on the
  stream details when the buffer is attached
- A queue stop releases only the buffers it claimed; a clear or a
replace still releases all
  of them, since it is discarding the items anyway
- Reusing a buffer that is already warm claims it for the session
reusing it
- Buffers are detached before being released, so one attached while the
old one is still
  being torn down is not dropped
- A stop that had no session of its own now tears nothing down, instead
of reading "no
  session" as "release everything"
- A stop cancels a prewarm that is still running, so it can no longer
attach its audio
after the stop has finished and leave the queue holding a provider's
stream

Needs music-assistant-models 1.1.205, which is already on `dev` via
#6086.

**Related issue (if applicable):**

- Companion PR: music-assistant/models#387
- Follow-up to #6077

## Types of changes

- [x] Maintenance / chore — `maintenance`

## Checklist

- [x] The code change is tested and works locally.
- [x] `pre-commit run --all-files` passes.
- [x] `pytest` passes, and tests have been added/updated under `tests/`
where applicable.
- [x] For changes to shared models, the companion PR in
`music-assistant/models` is linked.
- [ ] For changes affecting the UI, the companion PR in
`music-assistant/frontend` is linked.
- [x] I have read and complied with the project's [AI
Policy](https://github.com/music-assistant/.github/blob/main/AI_POLICY.md)
for any AI-assisted contributions.
- [ ] I have [raised a PR against the documentation
repository](https://github.com/music-assistant/music-assistant.io/blob/main/CONTRIBUTING.md)
targeting the main or beta branch as appropriate.