feat: bindings for simple extensions

[tokoko]

Adds python bindings for json schema of simple extensions.
Refactors extension registry to use new binding objects.

[tokoko]

I chose to go with python dataclasses rather than something like pydantic as codegen target to minimize external dependencies. On the other hand, I had to also include a converter to convert parsed yaml into generated dataclass objects as standard library can't do that out of the box.