Fix double sendspin bridges for devices with both Airplay and Cast

[MarvinSchenkel]

This PR makes the bridge evaluation idempotent for devices that both have Airplay and Cast protocols:

• Airplay is always preferred
• Chromecast bridges now subscribe to player and provider events to evaluate whether the cast bridge is still needed

So MA can now:

• Tear down the cast bridge and add an Airplay one when Airplay is detected (and vice versa). This also fixes the race condition where Cast registered before Airplay and left an orphaned (2nd grayed out) sendspin protocol on the universal player
• Auto clean up orphaned sendspin bridges.

This PR also surfaced the KeyError: 'player_id' bug which turned out to be a missing guard in the save_protocol_parent_id function.

[Copilot]

Pull request overview

This PR aims to make Sendspin bridge creation/removal for Chromecast devices idempotent when a device supports both Chromecast and AirPlay, with AirPlay preferred and automatic cleanup of redundant/orphaned bridges/config.

Changes:

• Add an idempotent evaluate_bridge path for Chromecast Sendspin bridges, including event-driven re-evaluation when relevant players/providers change.
• Prefer AirPlay bridges over Cast bridges when both are present under the same universal/parent player (and AirPlay is available).
• Add cleanup logic during universal-player restore to remove orphaned protocol player configs.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
music_assistant/providers/universal_player/provider.py	Adds cleanup for invalid/orphaned linked protocol player configs during universal-player restore.
music_assistant/providers/chromecast/sendspin_bridge.py	Introduces _should_have_bridge + evaluate_bridge, adds event subscriptions, and improves bridge removal cleanup.
music_assistant/providers/chromecast/provider.py	Switches bridge setup on discovery from setup_bridge to the new evaluate_bridge reconciliation flow.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

[marcelveldt]

I think for now this is fine to add like this but if we plan to add more bridges, we should have a generic bridge helper logic in the sendspin provider that can make the decisions per protocol