Feature: Make executors and feedbacks easier to use outside of the fuzzing loop

[Lukas-Dresel]

It would be nice to be able to use LibAFL components more easily outside of LibAFL's fuzzer harnessing (by which I mean the plug-and-play fuzzing loop) to allow for more reuse.
For example, I found myself ripping my hair out over trying to just run the forkserver with an observer to simply collect, aggregate and plot coverage. To do so, I had to provide types for fuzzers, feedbacks, schedulers, etc. even though none of those things were relevant for my use-case.

I ended up making changes like the ones in this PR in my own fork and it made it quite a bit nicer to use, now you can reuse some of the components and are only required to satisfy the directly needed type constraints for these components.

[domenukk]

@addisoncrump can you take a look? It might interfere with #2438 somewhat (?)

[domenukk]

It would be nice to be able to use LibAFL components more easily outside of LibAFL's fuzzer harnessing (by which I mean the plug-and-play fuzzing loop) to allow for more reuse. For example, I found myself ripping my hair out over trying to just run the forkserver with an observer to simply collect, aggregate and plot coverage. To do so, I had to provide types for fuzzers, feedbacks, schedulers, etc. even though none of those things were relevant for my use-case.

ideally the normal run_target would already be reusable / have minimal generic bounds/ have sensible Nop Variants for easy use.
But it might be a goal that's harder to achieve :D

[addisoncrump]

Sorry for the delay -- lots of IRL stuff right now. I will look at this tomorrow.

[domenukk]

Sorry for the delay, I think we can merge this.

[tokatoka]

wait, i'll check this when i refactor (or before) executor.
don't merge now