Refresh and types

[astrojuanlu]

• Converted some classes to auto_attribs=True to enhance type checking
• Almost fully strict MyPy mode

Still lots of TODOs, untested stuff, open questions... But it's a good start, I think. Will leave this open for a few weeks because it's unlikely that I'll be able to work on this in the immediate future, but at least it will serve as inspiration to others until I finish it.

[Sedictious]

Hello @astrojuanlu are you planning on continuing to work on this? If you want, I could try rebasing and continuing with the rest of the classes

[astrojuanlu]

I don't intend to keep working on this 🙏🏽 I had many open questions about what the best way to proceed would be.

to begin with, I love attrs but the whole @attr.s(auto_attribs=True, repr=False, frozen=True) was a bit annoying. maybe dataclasses is simpler? or even pydantic these days?

on the other hand, maybe the whole codebase should be automatically generated #81 from the schema, but I never made progress with that. the thing is that the CZML3 spec can produce very nested objects that are cumbersome to build.

this is an open problem for whoever takes over.