Add inline Git blame

[beeelias]

Summary

• add optional [editor] inline-blame support for current-line Git blame annotations
• render blame as muted inline virtual text with author and timestamp only
• skip blank lines, uncommitted blame records, and stale cursor-line results

Testing

• cargo check -p helix-term
• cargo test -p helix-vcs --features git
• cargo test -p helix-vcs
• git diff --check

[beeelias]

[RoloEdits]

There is also #13133 which uses gix-blame instead of shelling out.