Implement bounded caches e.g. LRU or TTL

[camsaul]

Like vanilla Clojure multimethods, Methodical multimethods assume dispatch values are bounded. There are some cases where this might not be desirable, e.g. if they're random numbers or something like that. See https://ask.clojure.org/index.php/10532/memory-leak-using-the-default-method-of-a-multimethod for more context.

Not sure what the actual use case for these would be but it seems like it would be good to support another use case that vanilla multimethods don't.