feat: allow --only-uncommitted to only see current non committed changes

[flamestro]

What changed

• allow --only-uncommitted to see non committed changes only

Why

• if users are working on multiple changes and did not push already, they are seeing previous commits as well in deff. However, it would be nice to have a way to just see uncommitted changes

Validation

• cargo check --locked
• Manual testing completed (if applicable)

Checklist

• PR is focused and scoped to one change
• Docs updated when behavior changes
• Breaking changes called out (if any)