[Repo Assist] fix: resolve oneOf/anyOf with single $ref to referenced type

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Closes #243

Root Cause

The v3 DefinitionCompiler already handles allOf: [$ref] with a single entry — it resolves the reference and returns the correct type. However, oneOf: [$ref] and anyOf: [$ref] with a single entry were not handled, so they fell through to compileNewObject() → obj.

These patterns are semantically equivalent to a direct $ref and are common in:

• Schemas generated by NSwag, Kiota, AutoRest
• OpenAPI 3.1 schemas using anyOf: [$ref] as the nullable type annotation (alongside nullable: true)

Fix

Add handlers for oneOf/anyOf with a single $ref entry immediately after the existing allOf single-ref handler, following the same pattern:

// Handle oneOf with single reference (resolves to the referenced type)
| _ when
    not(isNull schemaObj.OneOf)
    && schemaObj.OneOf.Count = 1
    && (schemaObj.Properties |> isNull || schemaObj.Properties.Count = 0)
    ->
    match schemaObj.OneOf.[0] with
    | :? OpenApiSchemaReference as schemaRef when not(isNull schemaRef.Reference) ->
        ns.ReleaseNameReservation tyName
        compileByPath <| getFullPath schemaRef.Reference.Id
    | _ -> compileNewObject()

Also extend the resolvedType inference guard to check oneOf/anyOf single-entry types when schemaObj.Type is absent.

Changes

File	Change
src/SwaggerProvider.DesignTime/v3/DefinitionCompiler.fs	Add oneOf/anyOf single-ref handlers and type inference
tests/SwaggerProvider.Tests/v3/Schema.TypeMappingTests.fs	Add 6 tests: oneOf/anyOf with string and int aliases, required and optional

Test Status

✅ Build: succeeded (0 errors, pre-existing warnings only)
✅ Unit tests: 328 passed, 0 failed, 2 skipped (all pass, 6 new tests added)
✅ Format check: fantomas --check passed on changed files

Integration/provider tests require a running Swashbuckle test server. The changed code is in the compile-time schema resolution path; it does not affect HTTP, serialization, or runtime behaviour.

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[Copilot]

Pull request overview

This PR fixes OpenAPI v3 schema compilation so that oneOf: [ $ref ] and anyOf: [ $ref ] (single-entry wrappers) resolve to the referenced schema type rather than incorrectly falling back to obj, matching the existing allOf: [ $ref ] handling in DefinitionCompiler.

Changes:

• Extend v3 DefinitionCompiler to resolve oneOf/anyOf with a single $ref entry to the referenced type (mirroring the allOf single-ref behavior).
• Improve type inference when schemaObj.Type is missing by looking into single-entry oneOf/anyOf subschemas.
• Add v3 unit tests validating oneOf/anyOf single-ref alias resolution for required and optional properties.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/SwaggerProvider.DesignTime/v3/DefinitionCompiler.fs	Adds single-$ref handlers for oneOf/anyOf and expands missing-Type inference to cover those wrappers.
tests/SwaggerProvider.Tests/v3/Schema.TypeMappingTests.fs	Adds tests ensuring oneOf/anyOf single-ref wrappers resolve to the referenced primitive alias type (including optional/value-type wrapping).

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