remove self type

[baszalmstra]

Remove Self type because its not available for python 3.8.

Bumps to 3.10 and adds typing-extensions.

Fixes #19

[Hofer-Julian]

Looks good, apart from the one nitpick.

Unrelated: would it make sense to move the content of pixi.toml into pyproject.toml?
Then we could remove some duplication.

[tdejager]

Looks good, apart from the one nitpick.

Unrelated: would it make sense to move the content of pixi.toml into pyproject.toml? Then we could remove some duplication.

We could, the only downside is that if you edit the pyproject.toml it is rebuilt, when running a pixi install.