This PR adds re-written difficulty calculators, which are based on uint256. It also adds a fuzzer + oss-fuzz integration for the new fuzzer. It does differential fuzzing between the new and old calculators.
Note: this PR does not actually enable the new calculators.
* added bls fuzzer
* crypto/bls12381: revert bls-changes, fixup fuzzer tests
* fuzzers: split bls fuzzing into 8 different units
* fuzzers/bls: remove (now stale) corpus
* crypto/bls12381: added blsfuzz corpus
* fuzzers/bls12381: fix the bls corpus
* fuzzers: fix oss-fuzz script
* tests/fuzzers: fixups on bls corpus
* test/fuzzers: remove leftover corpus
Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>
