cmp::parse_params exits the process on --help instead of returning #220

When --help is passed to cmp::parse_params, it calls process::exit(0) which kills the whole process. Found this while working on the fuzz targets, the fuzzer kept crashing because of it.
Workaround is to filter --help before calling parse_params, but ideally the function should just return the help text instead of exiting.

Not sure if this is worth a bigger refactor or just leaving the workaround in place, open to suggestions.
Example CI failure: https://github.com/uutils/diffutils/actions/runs/24710862259