Remove undefined arithmetics method.
Fixed VarInt serialization bug for the 0xffffffff number. Fixed VarInt sizeOf bug for the 0xffffffff number and added tests for VarInt edge cases.

The 4294967295 number (0xffffffff) was incorrectly serialized because the UnsignedInteger.MAX_VALUE.longValue() helper returned 4294967295 instead of expected 4294967296.

The VarInt.sizeOf() incorrectly returned 9 instead of 5 for the 4294967295 (0xffffffff) number.

See https://en.bitcoin.it/wiki/Protocol_specification#Variable_length_integer