ci: lint with swiftformat

[watt]

1. Adds a CI job that runs swiftformat --lint so that formatting is enforced.
2. Updates the pre-commit hook to use git-format-staged when formatting.
3. Removes the SwiftPM dependency on SwiftFormat, preferring mise.
4. Formats everything.

Recommend reviewing by commit to see the changes that aren't formatting.

Fixes #33

Checklist

• Unit Tests
• UI Tests
• Snapshot Tests (iOS only)
• I have made corresponding changes to the documentation

[jamieQ]

changes generally seem good to me. i have some personal qualms with the set of formatting rules used, but can deal with that in the future. i'm not super familiar with 'mise' – is that this tool?

[watt]

i'm not super familiar with 'mise' – is that this tool?

Yes, though we don't use the SPM backend. Mise is how we depend on Tuist.