Figure out if there's a reasonable way to shrink operations themselves

[nickelization]

Currently, we only shrink by removing entire operations, not by shrinking the operations themselves. Shrinking an individual operation can be quite tricky, however, because oftentimes later operations were generated based off the specific operations that came before them.

It may be possible to add some kind of optional "fix operation" callback that can attempt to modify later operations to make preconditions pass again after an earlier operation is shrunk, but this seems like a tricky proposition, and in practice we've found that the current shrinking method is sufficient; getting to a minimal set of steps to produce a failure typically makes it easy to understand failing cases even if the steps themselves are more complex than they need to be.

However, if anyone has any ideas or suggestions here, I'd love to hear them. It would be a cool feature to implement, if it turns out there's a good way to achieve it.