NLPCloud client integration (#81)

lots of kwargs! generation docs here:
https://docs.nlpcloud.com/#generation

This somewhat breaks the paradigm introduced in LLM base class as the
stop sequence isn't a list, and should rightfully be introduced at the
time of initialization of the class, along with the other kwargs that
depend on its presence (e.g. remove_end_sequence, etc.) curious if you'd
want to refactor LLM base class to take out stop as a specific named
kwarg?

requirements.txt

@@ -3,6 +3,7 @@
 cohere
 openai
 google-search-results
+nlpcloud
 playwright
 wikipedia
 huggingface_hub