Add type hints

[mariakimheinert]

We have started adding type hints with PR #91. For maintainability, we should add type hints (at least for all function inputs and outputs) throughout the entire system. Because the system is relatively small, this would be a great onboarding task for a new maintainer as it will help them develop an understanding of the system's architecture.

[mariakimheinert]

@Yanqiao4396 or @Ochirsaikhan, might this be something you would be interested in doing?

[gkapfham]

Hi @Yanqiao4396 and @Ochirsaikhan, I wanted to follow up with you again to see if you are interested in adding type annotations to the GatorGrade code base?

[Yanqiao4396]

Sorry for the late reply, I didn't turn on the notification on Github. After checking that, I feel I can do it these days. I can promise to finish that within 7 days