Addresses an issue where thinking signature validation fails due to model mapping and empty internal registry.
- Implements a fallback mechanism in the router to use the global model registry when the internal registry is empty. This ensures that models registered via API keys are correctly resolved even without local provider configurations.
- Modifies `GetModelGroup` to use registry-based grouping in addition to name pattern matching, covering cases where models are registered with API keys but lack provider names in their names.
- Updates signature validation to compare model groups instead of exact model names.
These changes resolve thinking signature validation errors and improve the accuracy of model resolution.
Improve the cache eviction routine to sort entries by timestamp using the standard library sort routine (stable, clearer and faster than the prior manual selection/bubble logic), and remove a redundant request-derived session ID helper in favor of the centralized session ID function. Also drop now-unused crypto/encoding imports.
This yields clearer, more maintainable eviction logic and removes duplicated/unused code and imports to reduce surface area and potential inconsistencies.
