Egglog simpler schedules

[pavpanchekha]

This PR updates the egglog backend in two ways:

• Updates egglog to use the new, simpler schedule syntax introduced in Simplify scheduling with pre-set schedule steps #1415. This makes the egglog backend work again.
• Adds the unsound schedule step, so that egglog now gets the same results as egg
  It also does various random cleanups—these aren't super high value because in the process I decided that the egglog backend is just too messy and needs a bigger cleanup, which will be a different PR.