Ship custom gtk4glsink plugin as part of API insead of normal gstreamer plugin. This avoids gstreamer plugin registry conflicts with gtk3 plugin and allows more customization.
A signal telling that "something somewhere changed" that is emitted multiple times per second (when bitrate changes). Not useful at all and a disaster performance-wise.
Not useful anymore since the player does 1s interval by default and now supports changing seek mode without stopping playback (unlike config which worked only when stopped).
Notify signal is a little problematic here as we already post a signal from player while jumping between APP and API contexts. Limit and disable it where not needed.
