Function detectSchema

Detect what kind of schema an unknown value is.

Detection order (most specific → least specific):

1. Zod v3/v4 — has ._def.type or .def.type string
2. Parseable — has .safeParse() or .parse() (Zod-like, yup, superstruct, etc.)
3. JSON Schema — has .type string or .properties object (structural markers)
4. None — not a recognized schema