CI: Split into static checks and tests

[Lorak-mmk]

Currently our main CI has 1 main job which performs static checks with cargo fmt / check / clippy and tests
If we split tests into separate job from static checks:

• CI code would be clearer and more readable imo
• Formatting / linting problems would not prevent tests from being run - this is sometimes frustrating when you push something, return to it later to see results of the tests and see that tests didn't run because of some formatting problem.
• Test more feature combinations without big penalty in running time: tests would probably still take more time
• Possibly speed up CI: tests don't have to wait for static checks