Changes related to creation of a modular backend in multiprecision [SyncWith: crypto3-multiprecision#70] #60

All 115 tests pass, 4 skipped in 6s

  36 files +  32   36 suites +32 6s ⏱️ +6s
119 tests +111 115 ✔️ +115   4 💤 +  4 0 ❌ -   8
576 runs +546 560 ✔️ +560 16 💤 +16 0 ❌ - 30

Results for commit 58ff868. ± Comparison against earlier commit bc423cc.