✨ pre-commit support for CUE / dagger

[jpadams]

What are you trying to do?

Add pre-commit support for CUE / dagger

https://pre-commit.com/#supported-languages
cue-lang/cue#363

Introduce a "test-only" mode.
Allow using cue fmt to detect whether changes are necessary without actually writing those changes to the target file. This is useful in pre-commit hooks and CI jobs to enforce proper formatting of CUE files.