Multiprecision refactoring: inverse mod and big_int improvements, checked big_uint operations #1363

All 7 263 tests pass, 6 skipped in 16m 17s

159 files + 1 159 suites +1 16m 17s ⏱️ -1s
7 269 tests +11 7 263 ✅ +11 6 💤 ±0 0 ❌ ±0
7 343 runs +11 7 337 ✅ +11 6 💤 ±0 0 ❌ ±0

Results for commit 46d55b1. ± Comparison against earlier commit 6783b80.