feat(openapi): support style and explode serialization for path parameters

[lx3133584]

Problem

Path parameters in OpenAPI 3.0 did not support style and explode serialization options, whereas query parameters already supported them.

Root Cause

In lib/spec/openapi/utils.js, plainJsonObjectToOpenapi3 forwarded style and explode properties on query/cookie/header containers, but omitted them for case 'path'.

Fix

Forward jsonSchema.style and jsonSchema.explode to the OpenAPI path parameter definition when specified.

Testing

• Added unit tests in test/spec/openapi/schema.test.js validating style and explode path parameter serialization with Swagger.validate().
• Verified all 268 test suites (100% coverage) and TypeScript type tests pass cleanly.

[Copilot]

Pull request overview

Adds OpenAPI path-parameter style and explode serialization support. It also introduces unrelated nullable-schema conversion with correctness issues.

Changes:

• Forward path serialization options.
• Test path serialization.
• Convert null-containing schemas to OpenAPI 3.0 nullable schemas.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
lib/spec/openapi/utils.js	Adds path serialization and nullable conversion.
test/spec/openapi/schema.test.js	Tests both behaviors.

Suppressed comments (2)

lib/spec/openapi/utils.js:558

• Converting type: 'null' to { nullable: true } does not preserve the schema. In OpenAPI 3.0, nullable only adds null to an explicitly declared type; without type, this schema is effectively unconstrained rather than null-only. Either reject this unsupported 3.0 construct or emit a constrained null-only representation instead of deleting its sole type constraint.

      if (value === 'null') {
        openapiSchema.nullable = true
        delete openapiSchema.type
        continue

lib/spec/openapi/utils.js:567

• For multiple remaining types, the generated schema has anyOf but no top-level type. OpenAPI 3.0 therefore does not apply the top-level nullable: true, and null is rejected even though the input explicitly allows it. Move nullable: true onto one typed anyOf branch (and remove it from the parent), then update the assertion to verify that representation.

        } else if (remainingTypes.length > 1) {
          openapiSchema.anyOf = remainingTypes.map(t => ({ type: t }))
          delete openapiSchema.type

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