feat: implement g2_add

[fgimenez]

Towards #11

I needed to remove some of the entries in the test vector from https://github.com/ethereum/go-ethereum/blob/ab49f228ad6f37ba78be66b34aa5fee740245f57/core/vm/testdata/precompiles/blsG2Add.json because of oddLength errors, indeed some of the values where 511 hex chars instead of 512 or 1023 instead of 1024, these are the wrong inputs:

odd length in expected of matter_g2_add_5, 511
odd length in expected of matter_g2_add_7, 511
odd length in expected of matter_g2_add_21, 511
odd length in input of matter_g2_add_33, 1023
odd length in expected of matter_g2_add_37, 511
odd length in expected of matter_g2_add_68, 511
odd length in input of matter_g2_add_71, 1023
odd length in input of matter_g2_add_83, 1023
odd length in input of matter_g2_add_91, 1023

I'll report upstream.

[Rjected]

nice, looks good to me!

[Rjected]

I'll report upstream

Yeah, makes sense, definitely do that