Implements an in-memory cache for loaded models with file modification
time tracking to ensure cache validity. Models are now cached after
first load and retrieved from cache on subsequent requests if the
underlying manifest file hasn't changed.
Key changes:
- Add ModelCache with get/set methods and modification time validation
- Cache models in GetModel() and check cache before disk load
- Move capabilities calculation to model loading time and store in model
- Update capability access to use cached field instead of runtime calculation
- Add test coverage for cache behavior and model loading
This reduces redundant model loading operations and improves response
times for model access.
Bruce MacDonald