test(xcatd): cover commands.log response redaction

Extracts the three command-log response subs and drives them. It checks the
request classification, the redaction of a bare passwd value, a secret split
across callbacks in either order, the password-content fallback, that a benign
response is kept, and that the finalizer preserves an earlier command's response
on a shared connection. It fails hard if a sub cannot be extracted.