chore: update to eslint v9

[06kellyjac]

Replaces #890
Replaces #893

Raises some warnings but fixing them isn't possible without formatting many files.
I'll do that in another PR.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.88%. Comparing base (38041ff) to head (b1c8cff).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #955   +/-   ##
=======================================
  Coverage   61.88%   61.88%           
=======================================
  Files          49       49           
  Lines        1805     1805           
=======================================
  Hits         1117     1117           
  Misses        688      688           

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[06kellyjac]

Ran into a couple roadblocks, holding off the styling fixes for now as the PR would be mega
@JamieSlome

[sam-holmes2]

@06kellyjac let me know if you need a review on this once conflicts have been resolved