feat: over-saturation stopping

Add over-saturation detection and stopping capability to GuideLLM CLI.

- Implement OverSaturationDetector with statistical slope detection
- Add OverSaturationConstraint for scheduler integration
- Add CLI flags --stop-over-saturated and --stop-osd
- Integrate with benchmark entrypoints and main CLI

Signed-off-by: Alon Kellner <[email protected]>

Author: AlonKellner-RedHat