test: add goccy/go-yaml tests and improve YAML marshal/unmarshal

[SVilgelm]

Add tests for goccy/go-yaml in RefOrSpec and Extendable types to ensure
compatibility with an alternative YAML library. This increases test
coverage and robustness for YAML handling.

Refactor Schema YAML marshal/unmarshal to use JSON as intermediate
format, simplifying the process and avoiding issues with extension
fields. Update UnmarshalYAML to support both go-yaml and legacy YAML
unmarshalers.

Remove some invalid or redundant test cases in singleOrArray tests and
fix minor formatting issues.

[Copilot]

Pull Request Overview

This PR adds tests for the goccy/go-yaml library and refactors YAML marshal/unmarshal implementations across several OpenAPI types to use JSON as an intermediate format. Key changes include the introduction of goyaml-based tests for types (e.g. RefOrSpec, Schema, etc.), refactoring of marshal/unmarshal methods to support both legacy and goyaml interfaces, and some cleanup of redundant test cases.

Reviewed Changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
validation_test.go	Added goyaml tests alongside legacy YAML tests for spec validation.
single_or_array_test.go	Refactored test helper and added goyaml tests for both JSON and YAML.
single_or_array.go	Updated marshal/unmarshal methods to use JSON intermediates for YAML.
schema_test.go, schema.go	Updated YAML handling using both yaml.v3 and goyaml libraries.
responses.{go,test.go}	Refactored responses marshal/unmarshal to use map-based fields.
ref_test.go, ref.go	Adjusted tests and ref unmarshaling methods to support goyaml.
paths.{go,test.go}	Updated YAML interface methods to adopt newer unmarshal function style.
extensions.{go,test.go}	Refactored extension handling to use JSON intermediates for YAML.
components.go	Minor adjustment to the regex pattern for validating component names.
bool_or_schema.{go,test.go}	Updated bool-or-schema tests and YAML unmarshal implementation.
README.md	Documented the new support for the goccy/go-yaml library.

Comments suppressed due to low confidence (1)

single_or_array_test.go:121

• There appears to be an extra trailing quote in the test data for the 'array of string for int' case. Please remove the extra quote to ensure the test data matches the intended JSON array format.

data:     []byte(`["first", "second"]"`),