* Adds repr and doctest of current behavior linkedlist in other/lru_cache
* Blocks removal of head or tail of double linked list
* clarifies add() logic for double linked list in other/lru_cache
* expands doctests to compare cache and lru cache
* [mypy] annotates vars for other/lru_cache
* [mypy] Annotates lru_cache decorator for other/lru_cache
* Higher order functions require a verbose Callable annotation
* [mypy] Makes LRU_Cache generic over key and value types for other/lru_cache
+ no reason to force int -> int
* [mypy] makes decorator a classmethod for access to class generic types
* breaks two long lines in doctest for other/lru_cache
* simplifies boundary test remove() for other/lru_cache
* [mypy] Annotates, adds doctests, and makes Generic other/lfu_cache
See also commits to other/lru_cache which guided these
* [mypy] annotates cls var in other/lfu_cache
* cleans up items from code review for lfu_cache and lru_cache
* [mypy] runs mypy on lfu_cache and lru_cache
