Enable strict type checked rules

[wjhsf]

When doing #383, I noticed that we extend @typescript-eslint/recommended-type-checked and @typescript-eslint/strict. There's also @typescript-eslint/strict-type-checked which is includes those two configs, plus a few additional type checked rules.

I also moved us from .eslintrc to the new flat config, just because we can!

[colincasey]

@wjhsf not sure what's going on with this PR but I tried to work around the bad resolutions in package-lock.json by just deleting and regenerating it locally with a fresh npm install. But, after doing that, I get errors when I execute npm run lint that eslint-config-prettier cannot be found.

[colincasey]

@wjhsf I'm not so sure about these changes. If you check the test output of https://github.com/salesforce/tough-cookie/actions/runs/8392570051/job/22985505761?pr=392 it looks like there are regressions introduced with the vows test suite which we're using as a sanity check for these types of refactorings.

Maybe a better approach is to disable all the new rules introduced with @typescript-eslint/strict-type-checked and have incremental PRs with each rule enabled + it's required changes?

[wjhsf]

Since we don't super care about how clean the vows tests are, I've just disabled the violated rules instead of fixing them, except one violation that's trivial.