Add caching for mapper

[caufieldjh]

The knowledge engine class includes a map_identifier function:

ontogpt/src/ontogpt/engines/knowledge_engine.py

Line 418 in e3a68ae

def map_identifier(self, input_id: str, cls: ClassDefinition) -> Iterator[str]:

This calls the NodeNormalizer API through OAK:
https://github.com/INCATools/ontology-access-kit/blob/0a734a8383943891173eaf8b1fd95cf4fde1f65e/src/oaklib/implementations/translator/translator_implementation.py

This process can take some time, especially when grounding many entities.

In some cases, we may not need to use the service at all: we may expect mappings to be uninformative.
In other cases, we may be grounding redundantly, and can cache our results.

requests-cache may help here.