fix: use player thread for player calls

[naveensingh]

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

Added onTaskRemoved() override to ensure internal calls to the player are done on the player thread. This is a quick fix for what appears to be a bug in media3 implementation (internal calls shouldn't assume the player runs on the main thread).

The whole keep player on background thread thing needs to be revisited.

Tests performed

• Playing, seeking items, closing app by clearing from recents

Closes the following issue(s)

• Closes Playback stops and app crashes when cleared from recents #298

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• All checks are passing.