V4Options class Null safety

V4Options stores the options passed into the v4 function. random is the random bytes to use to generate the UUID. Primarily used for testing, or recreating a UUID rng is the random number generator function to use. Defaults to UuidUtil.mathRNG namedArgs is a map of named arguments to pass to the RNG function positionalArgs is a list of positional arguments to pass to the RNG function