- Fixed rate-limit-utils to recognize and classify 'usage limit' errors as QUOTA_EXHAUSTED instead of transient.
- Added isUsageLimitError() utility function for unified detection of persistent quota limit errors across providers.
- Fixed Codex provider to return immediately on usage-limit errors instead of retrying, preventing unnecessary 5-minute delays.
- Removed usage.?limit pattern from TRANSIENT_MESSAGE_PATTERN to prevent misclassification of persistent quota errors.