Label the scheduler's core count as usable in diagnose

The number handed to the scheduler is what is left after the load limit
and the cgroup quota, not what the machine reports; the raw count and
each limit are on the "System resources" lines above it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PRfhXECP8wuY7qyLqRaXk3

Author: ondrejmirtes

src/Parallel/Scheduler.php

@@ -130,7 +130,7 @@ public function print(Output $output): void
 		[$cpuCores, $filesCount, $jobsCount, $usedNumberOfProcesses, $decision] = $this->storedData;
 
 		$output->writeLineFormatted('<info>Parallel processing scheduler:</info>');
-		$output->writeLineFormatted(sprintf('# of detected CPU cores:   %d', $cpuCores));
+		$output->writeLineFormatted(sprintf('# of usable CPU cores:     %d', $cpuCores));
 		$output->writeLineFormatted(sprintf('# of analysed files:       %d', $filesCount));
 		$output->writeLineFormatted(sprintf('# of jobs:                 %d', $jobsCount));
 		$output->writeLineFormatted(sprintf('# of spawned processes:    %d', $usedNumberOfProcesses));