fix(auth): avoid cooldown for request-scoped 401 request-faults

- Treat request-invalid/invalid-parameter 401 faults as request-scoped so auth/model cooldown is skipped.
- Export request-scoped/connection-lifecycle error codes and add helpers to explicitly create or mark request-scoped `Error`s.
- Improve request-fault detection by checking the raw message body when `Error.Code` formatting hides JSON payloads.

Closes: #4976