- Introduced `SetTransientErrorCooldownSeconds` to enable configurable cooldowns for transient errors (e.g., 408/500/502/503/504).
- Updated retry scheduling logic to use the new `nextTransientErrorRetryAfter` function.
- Modified config parsing to include `transient-error-cooldown-seconds` with support for disabling or defaulting to legacy behavior.
- Expanded tests to validate transient cooldown logic with various configurations and edge cases.
Closes: #3315