table test recovering the block parts from mempool

[rach-id]

          [could be a followup issue]

I like this test and have written similar style heavy weight random tests before. I think this is combining correctness testing and fuzzing however. It might actually be better if we have table driven tests for as many edge cases as we can think of, then have a fuzzer ontop

Originally posted by @evan-forbes in #1664 (comment)