Keyword arguments of pullbacks are unreachable in AD

[lkdvos]

Currently, while our pullback functions have some keyword arguments to control their behavior, there is actually not really a way to access these in the context of the various AD engines.
This is something we should try and think about a bit more, even though I am not really coming up with a lot of concrete suggestions for now.
I know we can take a bit of inspiration from what we tried in KrylovKit, but it might still make sense to rethink that interface a bit.