Function liftExampleToExamples

Lift OpenAPI 3.x singular example onto the plural examples key.

Two output shapes are spec-correct depending on the parent object type:

• "array" — Schema Object: examples: [example] (Draft 2020-12 plural).
• "map" — Parameter / Header / Media Type Object: an Examples Map keyed by name. The single value is wrapped under the synthetic key default to produce a valid one-entry map of one Example Object.

When both example and examples coexist the spec declares them mutually exclusive — example is dropped and examples wins.