[Fuzzing] Implement a Fp12 serializer to canonical serialization#454

To fix https://github.com/guidovranken/el-fuzzers/issues/7 we need a serializer to canonical representation similar to BLST: https://github.com/supranational/blst/issues/101. This would allow merging into Geth fuzzer as well. Note we have a towering switcher: https://github.com/mratsim/constantine/blob/1e34ec22929eaba7bcf1681350ec21aed8f370f7/constantine/math/pairings/cyclotomic_subgroups.nim#L675-L702 We might want to special-case this in a "fuzzing.nim" file as it might be that in the future Fp12 serialization is specified for the Whisk protocol that uses Fp12: https://ethresear.ch/t/the-return-of-torus-based-cryptography-whisk-and-curdleproof-in-the-target-group/16678