pub fn derive_job_count(jobs: impl Into<Option<usize>>) -> usize {
    let maybe_jobs = jobs.into();
    match maybe_jobs {
        _ if cfg!(debug_assertions) => {
            log::warn!("Debug mode always uses 1 thread!");
            1
        }
        Some(jobs) if jobs == 0 => {
            log::warn!(
                "Cannot have less than one worker thread ({jobs}). Retaining one worker thread."
            );
            1
        }
        Some(jobs) if jobs > 128 => {
            log::warn!("Setting threads beyond 128 ({jobs}) is insane. Capping at 128");
            128
        }
        Some(jobs) => {
            log::info!("Explicitly set threads to {jobs}");
            jobs
        }
        None => {
            // commonly we are not the only process
            // on the machine, so use the physical cores.
            let jobs = num_cpus::get_physical();
            log::debug!("Using the default physical thread count of {jobs}");
            jobs
        }
    }
}
Set the worker pool job/thread count.

Affects the parallel processing for a particular checker. Checkers are
always executed in sequence.
src/config/args.rs