Feat: add an example for spmc ring buffer

[solus161]

Description

This is an PR for the issue #101.

The example follows several other examples such as hello-single-latest-async. It features one producer and two consumers running at different rates and tries to simulate the lagging/dropped message behavior of the ring.

Related Issue

• [Add minimal example: hello-spmc-ring-async #101]

Checklist

• I have read the CONTRIBUTING.md document.
• My code follows the project's coding standards.
• I have added tests to cover my changes.
• All new and existing tests passed (make check).
• I have updated the documentation accordingly.