chore: replace depcheck with knip

[dbudzins]

Description

Depcheck was getting annoying with monorepo tools and refactoring. It doesn't work with any local imports besides relative paths, so tsconfig baseurl and paths all have to be manually added to the depcheck ignore file. See https://github.com/depcheck/depcheck/issues/564.

Knip does the same thing, but does take tsconfig and other environments into consideration. Additionally, knip uses a single, combined config file, which seems easier to manage than all of the fragmented depcheck files.

Steps completed:

According to our definition of done, I have completed the following steps:

~- [ ] Acceptance criteria met~ ~- [ ] Unit tests added~ ~- [ ] Docs updated (including config and env variables)~ ~- [ ] Translations added~ ~- [ ] UX tested~ ~- [ ] Browsers / platforms tested~

• [x] Rebased & ready to merge without conflicts
• [x] Reviewed own code

[github-actions[bot]]

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