[CICD] Improve test / fuzz execution criteria

[sea212]

All unit and fuzz tests are executed in any case, even if none of the actual source code was changed. A massive amount of required time for workflows can be reduced by selectively executing unit and fuzz tests.

Figure out a way to determine whether changes in relevant code happened and execute the job only in that case. As a bonus, selectively execute unit and fuzz tests only on files / crates that actually contain changes.