add support for $ref's in request bodies

[Southclaws]

Summary

Adds support for $ref'ing a requestBody

Referenced request bodies are resolved before operation analysis, preserving their requirdness, media type, schema, and validation document, etc..

Generated compatibility

• Generated model or method signatures: Operations whose requestBody is a local $ref now receive the same typed body parameter they would receive if the Request Body Object were inline.
• Query/path/header/body wire behavior: refs included now
• Generated runtime dependencies or features: none
• Configuration defaults or migrations: none
• Remaining unsupported OpenAPI shapes: External-document request-body, but I guess this would be wider work around $ref's in general

Validation

• Added or updated a focused fixture and behavioral regression test.
• Reviewed every changed snapshot; no unrelated churn is included.
• cargo fmt --check
• cargo clippy --all-features -- -D warnings
• cargo test --all-features
• Ran scripts/install-smoke.sh for packaging/dependency changes.
• Ran a targeted or full scripts/spec-compile.sh for generator changes.
• Updated README, rustdoc, or changelog for user-visible behavior.

Notes for reviewers

ai transparency: this was achieved using codex while generating a rust server for a project (radengine)

[vercel]

@Southclaws is attempting to deploy a commit to the lbl-rd Team on Vercel.

A member of the Team first needs to authorize it.

[lightsofapollo]

@Southclaws Cool! I'll take a look in a moment

[Southclaws]

thanks! for now, using the fork actively in https://github.com/Southclaws/rad/pull/1/changes#diff-6939ad63aa2db19c9744bcf201876151af31d4674260edaca29bd679babccf58 against this schema in case it helps validate more use-cases!

and now that I think of it, I have a rather mature 13k line schema that could be useful for battle testing this generator here in case it helps!

[lightsofapollo]

excellent- I'll try that schema too. Testing this pr now should land momentarily

[lightsofapollo]

nice- that openapi.yaml surfaced a few small things in the client and one larger thing in server generation. Appreciate it!