Backoff scheduler

[0x0f0f0f]

By now, this implementation uses an every-rule-every-time. A scheduler that identifies rewrites that are unperformant would make this implementation a lot faster.

From the egg paper https://dl.acm.org/doi/pdf/10.1145/3434304

By default, egg uses the built-in
backoff scheduler that identifies rewrites that are matching in exponentially-growing locations and
temporarily bans them. We have observed that this greatly reduced run time (producing the same
results) in many settings. egg can also use a conventional every-rule-every-time scheduler, or the
user can supply their own.