Same std::thread split as exhaustive32_midpoint; preserves each test's existing
failure behavior (abort for exhaustive32, stop-flag for exhaustive32_64).
manually checked modified files for errors, but not committing .clang-format due to the following warning:
>>> Setting `QualifierAlignment` to something other than `Leave`, COULD lead to incorrect code formatting due to incorrect decisions made due to clang-formats lack of complete semantic information. As such extra care should be taken to review code changes made by the use of this option.
