This PR improves the IsOnCurve methods for BN254 G2 points by:
* Clarifying its behavior the docstring, making it explicit that it
verifies both the point being on the curve and in the correct subgroup.
* Adding an in-line comment explaining the subgroup membership check
(c.Mul(Order)).
* Minor wording adjustments for readability and consistency.
Co-authored-by: Antonio Sanso <antonio.sanso@gmail.com>
* core/vm, crypto/bn256: switch over to cloudflare library
* crypto/bn256: unmarshal constraint + start pure go impl
* crypto/bn256: combo cloudflare and google lib
* travis: drop 386 test job