Duplicate Entry Handling (Fixes #179)

[CyanVoxel]

Initially this was intended to be a quick patch that ended up needing a bigger fix, especially when it came to conflicts with the workflows that I was unable to reproduce on my machine. Either way, I should really be making my changes via PRs in the first place...

This PR makes the following changes:

• Running "Fix Unlinked Entries" will no longer result in duplicate entries if the directory was refreshed after the original entries became unlinked.
• A "Duplicate Entries" section is added to the "Fix Unlinked Entries" modal to help repair existing affected libraries.
  • Having duplicate entries like this is not something that's supposed to happen in the first place, so this section here is not a long-term solution.

There were a couple bodges in this involving Path casting and applying # type: ignore to problematic lines that set off MyPy, false positives or otherwise.