Reduce time needed for mutation tests

[ricardoboss]

GitHub actions is a great tool to automatically run tests and analyze the codebase. One such test is the mutation test suite using infection.

The mutation test take the longest time in the entire pipeline, due to all the possible mutations that are tested. The more code gets added, the longer the mutation tests will take with exponential growth.

The goal of this issue is to reduce the time need to run mutation tests. One way would be to run mutation tests only on the git diff, like described at infection.github.io/guide/command-line-options.html#git-diff-filter.

Another option would be to not update the mutation score with every commit, but on a schedule, like this note describes: https://github.com/elephox-dev/framework/projects/1#card-83143011