Allow change vocabs for processor that take vocabs

[Logiquo]

Contributor: Yongda Fan (yongdaf2@illinois.edu)

Contribution Type: Processor

Description
Add retain and remove method to modify the code_vocab in the processors. This should facilitate the PyHealth agent to select or remove particular code it deteremines to be useful or not useful.

[jhnwu3]

Can we add a def add(self, vocabularies : set[str) operation as well? Just in case?

Understandably, no model can do this (yet). But, I can imagine a future where models simply add another row to the vocabulary embeddings within a model and do some type of continual learning/finetuning in the future as this is an active area of research in many conferences.