The Rust equivalent of json-schema-faker, scoped to what's actually
useful in Rust: resolves $ref (relative to whichever file references
it)/allOf, fills const/enum/default, and builds a value only for
properties listed in required - everything else is left out. For code
that has to construct a raw serde_json::Value against a schema it
doesn't own, instead of a typed struct.
Verified against continuum-schemas' real bambulab schemas manually, and
against local fixtures in tests (round-tripped through the jsonschema
crate to confirm the output actually validates).
