Narrowing a morph within a single type preserves the type-level morph representation

[ssalbdivad]

This test case is currently commented out because it fails at ark/type/__tests__/narrow.test.ts:115

it("narrows the output type of an morph within a single type", () => {
  const t = type("string")
    .pipe((s) => `${s}!`)
    .narrow((s): s is "foo!" => s === "foo!");

  attest<Type<(In: string) => Out<of<"foo!", Narrowed>>>>(t);
});

It is actually inferred as:

type Actual  = Type<of<"foo!", Narrowed>

Because includesMorphs in ark/schema/roots/morph.ts can't identify a morph within a single type.

To resolve this issue, includesMorphs would likely have to recurse directly to find a morph AST, or _distill would need to return a context of some sort that includes the distilled type as well as other info like whether a morph was encountered.

This change could be expensive in terms of static perf, so benchmarks should be run to ensure the cost is acceptable.