JSON Schema to OpenAPI v3.0.x Converter

Converts standard JSON Schema (draft-07, 2019-09, 2020-12) to an OpenAPI v3.0.x compatible Schema Object. Current stable version is 0.5.0, released irregularly with breaking changes (v0.3.0 removed built-in $ref handling). Key differentiators: focused solely on v3.0.x compatibility (not v3.1.x), handles specific JSON Schema features unsupported by v3.0.x — converting items from array to object, multiple types to oneOf, const to enum, null type to nullable, and default values to proper OpenAPI types. Does NOT dereference $ref; users must pre-process with a separate dereferencing library. Lightweight with no runtime dependencies.