Failure of "maximum unsigned values" test under Dart 2

[kaetemi]

The large "ubigint" value fails under Dart 2 (even when removing the "expect" test line - the query result value causes a failure) due to an issue parsing the unsigned 64bit value to an int. Dart int is a signed 64bit value.

I'm not sure if there's a clean way to cope with an unsigned 64bit value. BigInt may be a solution, but adds some complexity.

[tejainece]

BigInt is the only viable solution.