Handle the infinity point in EVM precompiles

[yelhousni]

The infinity point is represented by (0,0) in the EVM:

• [x] handle the edge cases in ECADD (AddUnified) that involve or should return (0,0).
• [x] handle the edge cases in ECMUL (ScalarMul and ScalarMulBase) that involve or should return 0 and (0,0).
• [ ] handle the edge cases in ECPAIR that involve (0,0).
• [x] handle the edge cases in IsOnCurve/Twist that involve (0,0).