Suggestion: Improve code snippet readability in documentation for easier copy-paste

Hi,

I wanted to suggest an improvement to the documentation format gently. While the `.. testcode::` blocks are great for testing examples, they present two minor friction points for new users:

1. **Readability**
The indented code blocks without syntax highlighting make it harder to scan/understand examples quickly

2. **Copy-Paste Experience**
When copying code directly from GitHub's rendered documentation:
- The extra indentation requires manual adjustment
- Hidden `.. testoutput::` blocks can accidentally get copied

Would you consider either:
- Adding triple-backtick (```python) code fences alongside testcode blocks
- Including a "Copy to Clipboard" button via Sphinx extensions ([like this one](https://sphinx-copybutton.readthedocs.io/))
- Adjusting indentation levels for better copy-paste ability

This would make it even easier for folks to:
1. Quickly try examples from the docs
2. Experiment with Tenacity's awesome features
3. Adopt best practices faster

I'm happy to help submit a PR if this aligns with the project's direction! Just let me know what approach you'd prefer.

Thanks!