Metric classes for metrics that do and do not use LLM assisted evaluation

[joeferraratonic]

#69 introduced a bunch of new metrics, some of which use LLM assisted evaluation and some of which do not. This issue is to create subclasses of the Metric classes for metrics that use LLM assisted evaluation and metrics that do not use LLM assisted evaluation so that only metrics that use LLM assisted evaluation need an LLM service to be used.