cleanStaleFiles method
Deletes stale *.g.dart files. Returns the number of files removed.
When dryRun is true, only reports; does not delete.
Implementation
int cleanStaleFiles({bool dryRun = false}) {
final stale = findStaleGeneratedFiles();
for (final f in stale) {
if (!dryRun) f.deleteSync();
}
return stale.length;
}