fix union quantification

[ssalbdivad]

these two test cases in @ark/regex currently fail because they rely on the distribution logic that references rely on:

it("quantified charset", () => {
  const S = regex("^[ab]{2}$");
  attest<Regex<"aa" | "ab" | "ba" | "bb">>(S);
});

it("quantified union group", () => {
  const S = regex("^(a|b){2}$");
  attest<Regex<"aa" | "ab" | "ba" | "bb", { captures: ["a"] | ["b"] }>>(S);
});