chore: remove eslint, use biome instead

[filmaj]

Many lines of code, little actual change. Perhaps the only thing worth taking a look at is the biome.json file that describes the lint and formatting rules.

Changes

• gets us out of the current tough situation where eslint v9 is new but we are stuck on v8 due to the airbnb eslint config being archived and unmaintained
• removes eslint, adds biome instead. https://biomejs.dev/ is way faster (eslint executes in dozens of seconds while biome executes in under a second) and only a single dependency compared to the complicated eslint buildchain
• moves all tests from .js to .ts (commonJS to ESM) <-- this took the most work, finally at least a vast majority of tests are typesafe now. caught many errors because of this (like invalid HTTP response mocks and things of the like).

[codecov]

Codecov Report

Attention: Patch coverage is 93.02857% with 183 lines in your changes missing coverage. Please review.

Project coverage is 91.61%. Comparing base (0374680) to head (becd125).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2006      +/-   ##
==========================================
+ Coverage   90.26%   91.61%   +1.34%     
==========================================
  Files          34       37       +3     
  Lines        7666     9924    +2258     
  Branches      381      633     +252     
==========================================
+ Hits         6920     9092    +2172     
- Misses        734      820      +86     
  Partials       12       12              

Flag	Coverage Δ
cli-hooks	95.23% <95.00%> (+0.28%)	⬆️
cli-test	95.39% <80.10%> (-1.54%)	⬇️
oauth	77.39% <75.00%> (+0.85%)	⬆️
socket-mode	58.22% <59.37%> (-1.37%)	⬇️
web-api	96.86% <95.83%> (+0.28%)	⬆️
webhook	96.65% <ø> (+1.37%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[seratch]

Nice! Too many changes to review but they should be safe. Regarding the changes under packages/web-api/src/types/response/, it's fine! but we may want to add the additional step that applies biome after generating in the script.

[filmaj]

Sounds @seratch , I will follow up with another PR for that shortly, and can test it out by running it in the PR, too.