Returns the positive integer represented by the eight bytes starting
at the specified byteOffset in this object, in unsigned binary
form.
The return value will be between 0 and 2<sup>64</sup> - 1, inclusive.
Throws RangeError if byteOffset is negative, or
byteOffset + 8 is greater than the length of this object.
Source
int getUint64(int byteOffset, [Endianness endian = Endianness.BIG_ENDIAN]);