feat(git): compact git grep output

[YOMXXX]

Summary

• add rtk git grep as a compact git subcommand with line-numbered grouped output
• keep machine/format-output flags like -l, --null, and --format on raw passthrough
• classify/rewrite git grep, git rev-parse, and git ls-files; the latter two continue through existing passthrough

Fixes #2495

Verification

• cargo +1.93.0 fmt --check
• git diff --check
• cargo +1.93.0 test --test git_grep_test -- --nocapture
• cargo +1.93.0 test test_rewrite_git_grep_and_passthrough_git_readers -- --nocapture
• cargo +1.93.0 test test_git_grep_passthrough_flag_detects_machine_output -- --nocapture
• cargo +1.93.0 clippy --all-targets
• cargo +1.93.0 test --all -- --skip small_grep_not_worse_than_plain