Coq 8.15 compatibility

[haansn08]

This pull requests makes the changes necessary to build the project with Coq 8.15:

• Replace omaga with lia.
• Use #[refine] attribute where necessary
• Depend on https://github.com/uds-psl/base-library (with some fixes).

[yforster]

Thank you, it's great to see that you're interested in the project!

Lots of code from here was integrated into https://github.com/uds-psl/coq-library-undecidability/, but I think not everything.

Depending on what you're after, it might be interesting to have a look at the library, there the code should be compatible with every published Coq version.