Fix update checker promoting downgrades, other followup improvements

[LostLuma]

Some improvements to my recent PRs:

• Add version of available loader update to the update text (image)
• Resolves Mod menu still keeps saying "Update Available" despite me downloading 3 stuff that were needed for the update #714 by checking whether the update Modrinth tells us about was released more recently than the one we're on
  • This should fix all cases except when people release updates out of order, but that seems unlikely
• Changed the way update checker threads are created so we can use more lightweight virtual threads
  • This will need two changes on the 1.20.4 branch:
  • Create platform threads in the update checker thread factory
  • Use Executors.newCachedThreadPool instead of newThreadPerTaskExecutor, or whatever you prefer

Since we need to do two requests to the Modrinth API I've refactored the update checker to run these in parallel in their own threads (which is why I did pt. 3) so it is hopefully not any slower than before.