Improve serialization bytes from variant

[conr2d]

Changes

• Check bytes size before serialization
  Restore check size condition that seems to be deleted by mistake

• Strip 0x prefix during bytes serialization
  Allow hex string for byte array to contain 0x prefix

• Parse odd-number length hex string during bytes serialization
  1FF will be serialized as 1F, because last digit is ignored when the length of string is odd. Unless throwing an exception for odd-length hex string, it had better serialize 1FF as 01FF to have intended value.