fix(git): respect combined -n log limits

[fengjikui]

Summary

• Fixes git log -n<N> combined form silently truncated to 10 commits #2665.
• Treats combined git log -n<N> arguments, such as -n20, as explicit user limit flags.
• Parses the combined short-option form so RTK does not inject/default-filter the output down to 10 commits.

Test plan

• cargo run --quiet -- git log -n20 | rg -c '^---END---$|^[0-9a-f]{7,} ' before fix -> 10; after fix -> 20\n- [x] cargo fmt --all\n- [x] cargo clippy --all-targets -- -D warnings\n- [x] cargo test cmds::git::git::tests -- --nocapture\n- [x] cargo test\n\n## Notes\nThis keeps the existing handling for -20, -n 20, --max-count=20, and --max-count 20 unchanged.