macosx: Load library gracefully

Two key changes in this MR:

1. Add detection for heavy-hitting library change notifications and throttle them (< 500 ms)
2. Display a blurred loading overlay view on the library view when it is loading lots of content, preventing jumping around of views and items
3. Temporarily stop checking for changes until the library state has stabilised, preventing the application from becoming unresponsive

After changes:

Screen_Recording_2024-02-01_at_16.05.47

Before changes:

Screen_Recording_2024-02-01_at_16.21.35

Signed-off-by: Claudio Cambra developer@claudiocambra.com