Returns the positive integer represented by the eight bytes starting
at the specified
byteOffset in this object, in unsigned binary
The return value will be between 0 and 264 - 1, inclusive.
Throws RangeError if
byteOffset is negative, or
byteOffset + 8 is greater than the length of this object.
int getUint64(int byteOffset, [Endian endian = Endian.big]);