Migrate to ESLint 9 and ESLint flat config

[acelaya]

Depends on https://github.com/hypothesis/frontend-toolkit/pull/50

Update project to ESLint 9 and migrate ESlint config to flat format.

This migration is introducing a few side effects:

• All // eslint-disable comments which do not disable anything have been removed, as they are now reported as warning.
• Error variable removed from catch blocks where the error is not used, as they are now reported as unused variables.
• Some eslint plugins needed to be updated:
  • @typescript-eslint/... packages replaced by typescript-eslint and updated to v8
  • eslint-plugin-react-hooks updated to v5
  • eslint-plugin-mocha updated to v10.5
  • eslint-plugin-react updated to v7.37
  • eslint-config-hypothesis updated to v3

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.42%. Comparing base (6a6e3ce) to head (d0df1ca). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6615 +/- ## ======================================= Coverage 99.42% 99.42% ======================================= Files 270 270 Lines 10175 10175 Branches 2419 2419 ======================================= Hits 10117 10117 Misses 58 58 ```

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