Improved case macro

[LasterAlex]

Inspired by this message.

Although the code for case! was fully rewritten, there are no breaking changes!

The goal was to make the case! pattern matching the same as the rust pattern matching, and I think it's pretty close for dptree purposes!

Sad that it's almost impossible to infer the type of None, but it's fine

I think the tests cover all of the new use cases