refactor(bench): improve utils.rs safety, error handling, and docs (#14057)

- Replace `unwrap` and `expect` with `anyhow::Result` for safer error handling
- Add contextual error messages using `anyhow::Context`
- Fix `home_path` on Windows by using `USERPROFILE` instead of `HOMEPATH`
- Ensure process helpers (`run_collect`, `run`) return `Result` instead of panicking
- Improve parsing logic in `parse_max_mem` and `parse_strace_output`
- Add documentation comments for all public functions
- Add best-effort cleanup and resilience against malformed input