Chore: Renamed Cache to LRUCache and extracted an interface and put under the old name to allow other implementations to be tested.

- Found and fixed minor bug where we tested max weight against count() instead of weight
- Found and fixed minor issue with possible long overflow.
- Adjusted tests but made explicit the ones who rely on the `LRUCache` implementation to test if settings are applied correctly.
While CacheBuilder#build() returns a `Cache` it still always returns the `LRUCache` implementation

Author: mjmbischoff