perf: Optimize page loading

[TheBobBobs]

Summary

Change search_library to only fetch entry.id.
Add get_tag_entries method to Library. Returns a dict[tag_id, set[entry_ids]]
Change update_thumbs to not fetch all tags for entries on page and instead use the above method to only check the tags it cares about.
move signal connection for item_thumb out of update_thumbs and into its init method.

This brings page load from 200ms->4ms

Tasks Completed

• Platforms Tested:
  • Windows x86
  • Windows ARM
  • macOS x86
  • macOS ARM
  • Linux x86
  • Linux ARM
• Tested For:
  • Basic functionality
  • PyInstaller executable