Crypto.VerifyConstant time bytes comparison.
bytes b0 b1 is true iff b0 and b1 are equal. Raises Invalid_argument if b0 or b1 are not of the same size.
bytes_16 b0 b1 is true iff b0 and b1 are equal. Raises Invalid_argument if b0 or b1 not made of 16 bytes.