v0.4.1 of vesper_player_external_playback

Optional external playback integration for Vesper Player Flutter hosts. Changelog excerpt: ### Breaking Changes - The Android plugin package and all external-playback channels now use the `io.github.umbrella22`reverse-DNS root. No old channel aliases are registered. - The external playback Flutter package now requires Flutter 3.44.0 or newer. ### Changed - Material widgets are imported through the official `material_ui`package. - The `material_ui`dependency now uses the stable 1.0 release. - Android build tooling now uses Kotlin 2.4.10 and kotlinx.coroutines 1.11.0; the native exte[...]