Attach the parent album to imported album tracks (#6111)

# What does this implement/fix?

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Some providers nest their tracks inside the album object and leave the
(redundant) album off each track. Qobuz and YTMusic both do this, so
tracks added by the album track import landed in the library with no
album at all, showing up unfiled with disc and track number 0.

Both call sites already hold the album and now pass it down, so no extra
provider request is made. A caller that does not hold it falls back to
get_album once per import rather than once per track. Existing unfiled
tracks are repaired on the next import, the same backfill the library
track sync already does.

**Related issue (if applicable):**

- related issue https://github.com/music-assistant/support/issues/6254

## Types of changes

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- [X] Bugfix (non-breaking change which fixes an issue) — `bugfix`
- [ ] New feature (non-breaking change which adds functionality) —
`new-feature`
- [ ] Enhancement to an existing feature — `enhancement`
- [ ] New music/player/metadata/plugin provider — `new-provider`
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected) — `breaking-change`
- [ ] Refactor (no behaviour change) — `refactor`
- [ ] Documentation only — `documentation`
- [ ] Maintenance / chore — `maintenance`
- [ ] CI / workflow change — `ci`
- [ ] Dependencies bump — `dependencies`

## 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.
- [ ] 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.