♻️ Name the matcher factories getMatcher / getMatcherW

Drop the strict/widened aliases from src/index.ts so the factories are
exported under their own names, and align the type tests, the autocomplete
probe (which now imports the public surface from ./index.ts) and library.md
with them.

Also correct the widened-overload comment: the excess-property check does not
apply to a generic P, so MatcherWidening's keyof guard — not the closed
constraint — is what rejects keys outside T/_, as library.md already
documented.

src/index.ts

@@ -1 +1 @@
-export { strict, widened } from "./primitive.ts";
+export { getMatcher, getMatcherW } from "./primitive.ts";