Fix Cast players ignoring media errors and the receiver app setting (#5622)

# What does this implement/fix?

<!-- Quick description and explanation of changes. -->

Two small fixes for Cast players, found while investigating a separate
issue.

1. When a Cast device fails to play what it was given, it tells us, but
Music
Assistant ignored the message. The player just went quiet and nothing
was
logged. Now a warning is written saying which player failed and what it
was
trying to play. This would have cut the investigation on the linked
issue from
two weeks to one log file.

2. The "Use Music Assistant Cast App" setting was ignored whenever the
device
was already running the other receiver app. Changing the setting
appeared to
do nothing, which sent the investigation down the wrong path. Now the
app the
user picked is always the one used.

**Related issue (if applicable):**

- related issue <link to issue>

## 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.

---------

Co-authored-by: Claude <[email protected]>