fix: hoist nested definitions to top-level components/schemas

[Upadhyay-Om]

Fixes #639

Problem

When using addSchema() with nested definitions, fastify-swagger silently deletes the definitions block during OpenAPI conversion. Any $ref pointing into those definitions ends up dangling — Swagger UI throws a "could not resolve pointer" error even though Fastify's runtime handles it perfectly fine.

Fix

Two things needed fixing:

• Before deleting definitions, each nested entry now gets hoisted up to top-level components/schemas under the key {parentName}-{defName}. The deletion then becomes safe since nothing is lost.
• The $ref rewrite regex was too strict — it couldn't handle schema IDs that contain slashes (like URLs). Switched the capture group to a greedy match so it handles the full ID correctly.

Test

Added a test in test/spec/openapi/refs.test.js using the exact reproduction case from the issue — registers a schema with nested definitions, references it via $ref in a route, and asserts both that the hoisted schema appears in components/schemas and that the $ref path is rewritten correctly. All existing tests still pass at 100% coverage.

Related: #676

Checklist

• run npm run test && npm run benchmark --if-present
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin and the Code of conduct

[mikaelkaron]

Not had a close look at the code yet but wanted to make you aware of #676. I don't see you having the same problems but could be worth while taking a quick read of the comments.