Polish and Performance

This update is all about polishing the UI, fixing bugs, and improving performance.
It contains countless changes under the hood and various improvements on the surface.
The various tagging related sidebars have all been replaced with the same design that was added in the last version and the entire multi-threading implementation has been reworked to be faster, more efficient, and less crashy.

•  moved to godot 4.3
• switched from my own thread "management" to GD4's WorkerThreadPool
• image viewer now preloads the next image in both directions
• lots of ui polish
• fixed various possible crashes, especially in large dbs
• various performance improvements, especially in large dbs

The development branch has been merged into the main branch, which now reflects this version of the program.