perf: implement caching to thumbnail render

[MichaelTj02]

Summary

Reworked thumbnail rendering pipeline and added queue-based caching saving previously rendered thumbnails outside of the viewport range. Fixed previous unstable rendering when scrolling up and down aggressively.

Type of change

• Feature
• Fix
• Other (perf)

How was this tested?

• Ran uv run main.py
• Open preprocessing module and import images
• Select the render thumbnail option
• Scroll up and down all the way to the end, then back to initial cursor location
• Checks:
  -Previously rendered thumbnails stays there. If cache exceeds size, check if thumbnail is deleted and re-rendered.
  -See if aggressive scrolling crashes the app