Add mutation testing in the CI

### Is your feature request related to a problem?

I’d like to improve ArkScript test suites. We already have coverage, but that only tells us the code was executed, not that it’s correct.

### Describe the solution you would like

To improve our tests, I’d like to add mutation testing (along side the existing fuzzing and coverage).

The idea would be to add a job running in parallel with the valgrind job. The idea is to run mutation testing on a single OS with a single compiler, to report how many tests should be improved.

https://www.youtube.com/watch?v=lhcXAnNgzlo

### Is it a big modification to the language? Leave it if you don't know

- [ ] Breaking change
- [ ] Compiler/syntax modifications
- [ ] Runtime modifications (standard library, modules, packages...)