Refactor: Call information should be stored in a single type #88
Description
We currently store call information in various types, each with small specialization, e.g., ChainedWaiterCallInfo, WaitCallInfo, etc. See attached screenshot (which might not be complete):
We should refactor this so we avoid code duplication. We could have common and a specialized fields, and we should implement getters on these.
Having separate types led to a lot of duplicated work in #84.
#79 works around it (for Python waiters) by introducing a CallInfo enum, but this should be removed as part of this refactoring.