refactor(providers): 🔨 replace interactive re-auth with permanent credential expiry

- Remove the complex re-authentication queue system (`_reauth_queue`) and associated background processors to prevent blocking operations.
- Implement a permanent expiry mechanism where credentials returning invalid grant or unauthorized errors (HTTP 400/401/403) are immediately removed from rotation.
- Disable attempts to trigger interactive OAuth flows during proxy operation; re-authentication now explicitly requires manual intervention via `credential_tool.py` and a service restart.
- Standardize "fail-fast" error handling and logging across Google, iFlow, and Qwen authentication providers.

Author: Mirrowel