Clarify reference comparisons when sorting by command

[pederbe]

Summary

Label command-sorted comparisons as faster than, slower than, or as fast as the reference, and identify the reference row. Preserve command order and the existing ratios.

Fixes #811.

Testing

• Added a deterministic CLI regression covering faster, slower, and equal times, custom command names, command order, and one or multiple runs. Confirmed it fails before the fix and passes afterward.
• cargo test --locked: 98 tests passed on Windows GNU with Rust 1.98.1.
• cargo fmt --all --check: passed.
• cargo clippy --locked --all-targets: passed with warnings in existing code and the Windows toolchain.
• Independent static review: no actionable findings.

Linux, macOS, and minimum supported Rust were not tested locally.