Convert eslint config to flat format

[AndreasArvidsson]

Eslint has a new flat configuration format

References:

• https://eslint.org/docs/latest/use/configure/migration-guide
• https://medium.com/ekino-france/migrate-to-eslint-9-x-29727f790249

Remove ESLINT_USE_FLAT_CONFIG=false from:

• pre-commit.yml
• package.json

I have already done this migration on my own andreas-vscode extension that we can use as a reference. Note that this has only a single config so it's much simpler than the Cursorless mono repo.