Mixed work on scaling equality saturation to tiling, mm, etc

[Bastacyclop]

Includes:

• tests and benchmarks for reordering and tiling
• code for direct e-class substitution, but the code is broken and not maintained
  • should this be merged in or put on the side?
• hash-consing for nats and types
• basic e-class filtering algorithm
• EGraphDot can now only print e-classes which are reachable from a set of given ones
• extraction of random terms from an e-graph
• hash-consing for pattern substitutions (can save a lot of RAM usage but does not help CPU usage as-is)
  • should this be merged in or put on the side? it should at least be optional
• NotFreeIn named rewrite rule conditional
• ProveEquiv builder
• directed rewriting prototype implementation, but it is not correct in the general case
  • should this be merged in or put on the side?
• rewrite rule Scheduler similar to egg`s design
• e-graph TypeCheck procedure (does not check everything but can catch bugs)
• many rewrite-rules, some of them might be questionable
• experiments with >> function composition combinator
• examples of beta-reduction and eta-reduction subtleties
• initial experiments rewriting MM and Harris applications