chore: upgrade eslint to v9.10.0

[iambumblehead]

hello, this PR updates eslint to version 9.10.0 so npm install no longer shows red audit warning messages.

• eslint 9 requires "eslint.config.js" added here,
• xo is removed because it does not support eslint 9 Upgrade to ESLint 9 xojs/xo#757,
• eslint-config-xo-lass exports an eslint 8 config, however its "rules" are usable with eslint 9 here,
• unicorn is added as adependency, because some of its eslint rules are used by eslint-config-xo-lass,
• many new and maybe pre-existing lint errors are raised --no effort is made to resolve the errors in this PR,
• npm run lint fails because of the lint errors --no effort is made to resolve this,
• because npm run lint fails, the husky commit hook fails

Hopefully this PR will be useful so that project owners may apply any remaining changes in ways they prefer.

Thank you :)

Checklist

• I have ensured my pull request is not behind the main or master branch of the original repository.
• I have rebased all commits where necessary so that reviewing this pull request can be done without having to merge it first.
• I have written a commit message that passes commitlint linting.
• I have ensured that my code changes pass linting tests.
• I have ensured that my code changes pass unit tests.
• I have described my pull request and the reasons for code changes along with context if necessary.