Initial Rover testcases - stressing common sub-expression aware extraction

[cowardsa]

We include multiple e-graphs for each test case based on e-graphs grown until increasing iteration limits - good extraction algorithms will ensure monotonicity - namely as the e-graph grows the cost should reduce - this is not true for naive ILP implementations.

Three testcases added:

1. MCM 3,7,21 - from O. Gustafsson, “A difference based adder graph heuristic for multiple constant multiplication problems,”
2. FIR Filter - from C. Lee, M. Potkonjak, and W. H. Mangione-Smith, “MediaBench: A tool for evaluating and synthesizing multimedia and communications systems,”
3. Box Filter - randomly generated testcase for constant factorization

[mwillsey]

Thanks Sam! This will be super valuable.