Auxiliary tooling: examples-scaffold + examples-diff

Part of #4831.

RFC: https://github.com/Azure/azure-rest-api-specs/blob/rfc/unified-examples-format/documentation/rfc/unified-examples-format.md

Auxiliary example tooling.

### Scope
- **`examples-scaffold`** — generate faked initial examples from the API surface, **replacing OAV's faked-example generation**.
- **`examples-diff`** — show what changed in an example between versions.

Depends on #4832 (schema).

Start by reading the unified examples RFC at documentation/rfc/unified-examples-format/rfc and inspect dependency #4832 for the schema. Then trace OAV's faked-example generation to understand what examples-scaffold replaces. Done means the scaffold and diff tooling described in the scope are implemented against the agreed schema.

Written by the indexing model from the issue text.