Test whether K1 and K2 form coset generators for BLS12-381

[kevaundray]

[CPerezz]

Starting by this resources that @decentralisedkev found: https://math.stackexchange.com/questions/507743/two-elements-are-in-the-same-coset-of-s-iff-their-difference-is-in-s , we will find and test generators and then, hardcode them into the repo as suggested in #131

[CPerezz]

To check if the difference is in S, we would need to check them order. But which is the order of the coset that we're expecting to get?

[CPerezz]

Same as #131