[6.0] Migrate from ESLint to Biome

[C-Lodder]

Summary of Changes

This migrates linting from ESLint to Biome, for 2 simple reasons:

1. Performance - Biome is at least 15x faster than ESLint due to the fact it's written in Rust and it multi-threadded.
2. Less dependencies - ESLint requires multiple plugins to work with languages and frameworks/libraries, whereas Biome supports them out of the box.

As part of this PR, I've also run the built-in formatter to try and use concise coding standards across the board.

To-Do

• Fix some remaining CSS lint issues
• Migrate CSS ordering rules
• Remove lint:css task from package.json
• Update Github action

@Fedik @dgrammatiko Would be nice to get your thoughts

[laoneo]

Did you add a line length? Would probably make sense to increase it, to have less changes in this pr.

[C-Lodder]

@laoneo The default is 80, which I believe is the same as ESLint.

Happy to increase this if you'd like a specific value, although 80 is generally considered a good number.

[laoneo]

If I remember correctly we were going in the past with 150. But can't find any evidence right now. Perhaps @wilsonge can shed some light here. Personally, I find 80 to close.

[laoneo]

These here are definitely incorrect.

[LadySolveig]

Should the lint:css script option perhaps also be removed?
If I saw it properly, the command would no longer work either.

[C-Lodder]

Yeah, I'll remove it eventually. Firstly need to port over the CSS ordering rules to Biome (if it's supported)

[C-Lodder]

@laoneo Biome doesn't support .scss files, only .css, so shall I re-add the stylelint to cater for them?

[laoneo]

Looks like then, otherwise there is a better alternative.