Added a Skill to examine the code snippets in markdown files.

[happyhuman]

Link to Issue or Description of Change

Describe the change:

Problem:
Some of the AI-generated code snippets may not be syntactically correct, or runnable. We need to identify them.
Issue: #6211

Solution:
This PR provides a Skill to examine the existing code snippets in a given markdown file (or a folder containing multiple markdown files) and check whether they load properly and/or run. It generates a report at the end with its findings.

Testing Plan

Manual End-to-End (E2E) Tests:
I tested the skill against a number of different existing markdown files under docs/guides using both Gemini and CloudCode. For instance, I use the following prompts in CloudCode & Gemini:

• Verify the code snippets in docs/guides/agents/llm_agent/single_turn.md
• Verify all the code snippets in all the markdown files in docs/guides/workflow

I also simultaneously used both Gemini and CloudCode to improve the skill.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.