Refactor and clean Conversions

[dem1995]

Overview:
aggregate_types fails typechecking and has redundancy

Intended outcomes:
Simplify aggregate_types.py from a user perspective; improve type-checking

Features:

• (aggregate_types.py) Update method names to be more sensible; merge relevant methods. Mark old methods as deprecated #15
• (conversions module) Ensure pyright conformance #16
• (Optional) make Conversions its own submodule