distance function
Calculates the euclidian distance between two vec3's
@param {ReadonlyVec3} a the first operand @param {ReadonlyVec3} b the second operand @returns {Number} distance between a and b
Implementation
double distance(List<double> a, List<double> b) {
final x = b[0] - a[0];
final y = b[1] - a[1];
final z = b[2] - a[2];
return hypot([x, y, z]);
}