fix: unwrap single non-object array items in allOf

[RomiRand]

Fixes #23837

This PR unwraps the entry of an allOf composed schema, if it is the only (non-object) item.

---

Summary by cubic

Normalizes allOf by unwrapping a single non‑object sub‑schema and turning null entries into nullable, fixing array item resolution and preventing invalid inline models. Renames the rule to SIMPLIFY_ONEOF_ANYOF_ALLOF and enables it by default. Resolves #23837.

• Bug Fixes
  • Simplify allOf in OpenAPINormalizer: remove null entries by setting nullable, unwrap a single non‑object sub‑schema, skip when $ref is present, and clear allOf for primitive/boolean types in OAS 3.0; also normalize array items using the normalized schema.
  • Added tests and YAML covering allOf simplification (including single-schema enums); updated docs/configs and test options to the new rule name.

^{Written for commit ffaeff5. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

2 issues found across 3 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[jpfinne]

@RomiRand could you move the code to the OpenApiNormalizer?

[RomiRand]

@RomiRand could you move the code to the OpenApiNormalizer?

@jpfinne Oh sure didn't realize, it's a big project 😅 I gave it a shot, ptal. Gotten bigger than anticipated, thought it makes sense to integrate with the existing oneOf/anyOf handling.. Lmk if a bigger diff like this should be avoided, or if renaming SIMPLIFY_ONEOF_ANYOF is too much of a breaking change