style: Action and Observation use schema for unifying

[iFurySt]

This PR only changes the String Literal of Action and Observation to the schema.ActionType and schema.ObservationType. but I opened the Black Formater, so the change seems like a lot. 😄

[iFurySt]

are you going to merge this? unifying constant

[rbren]

@iFurySt sorry I missed this one! This seems like a great change--sorry for the rebase pain

[iFurySt]

okay, i handle it later🥳

[iFurySt]

@rbren hard to catch up~ appreciate it if you have time to merge it into the main branch.

[rbren]

Thank you!