Improve Type Consistency Internally

[StandingPadAnimations]

While we did move towards annotations for functions in MCprep (see #425), it seems that we don't properly guarantee these types internally. In addition, there are areas where types can be a bit ambitious, but no checks exist for said types. This means that our type annotations aren't always correct as a source documentation for developers.

In addition, developers with editors that have strict static analysis built in as their LSP will deal with a multitude of warnings and errors relating to types. As an example, here's what my editor shows with the find_from_texturepack function:

I'm not suggesting we go all out and disallow dynamic typing (although BpyBuiild does that, but it has the benefit of starting that way), but we can take some steps to improve type consistency.

Some ways we can improve type consistency:

• Guaranteeing the types we say a function will return will be the types a function returns
  • Performing isinstance checks
  • Checking for None
  • Converting or gracefully return an error if needed
  • Etc.
• Covering cases where types may not be provided fully, such as with bpy utilities
  • In BpyBuild, we use a typing.cast in areas where a function doesn't provide a type signature or is ambitious, mostly for argparse arguments
  • One particular sore spot with this issue is env.json_data, due to the complexity of the type needed. A good option would be moving from a raw dictionary to a class with the JSON data, though such a migration would have to be done incrementally