[Refactor] Investigate/Implement refactor to use anoncreds-rs types instead of internal anoncreds_types crate

[gmulhearn]

As discussed in our recently community call, we want to look into refactoring such that anoncreds-rs types are used throughout the codebase, instead of our copy-paste thin layer of the types anoncreds_types.

Some discussion is found here.

Open questions:

• how much "extra dependencies" would this force on consumers would want to compile without any features?
  • If it's a concerning amount, then we will want to request that anoncreds-rs create their own dedicated "anoncreds_types" crate in their repo