[Lang] Move real function out of the experimental module

[lin-hitonami]

Issue: #

Brief Summary

🤖 Generated by Copilot at 8c46960

This pull request updates the real_func examples and tests to use the stable ti.real_func decorator and the new vector, matrix, and field APIs. It also refactors some code for readability, performance, and consistency, and removes the deprecated experimental module.

Walkthrough

🤖 Generated by Copilot at 8c46960

• Remove experimental module and move real_func decorator to top-level taichi module (link, link)
• Update all examples and tests that use real_func decorator to import it from taichi module instead of experimental module (link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link)
• Delete python/taichi/experimental.py file as it is no longer needed (link)

[netlify]

✅ Deploy Preview for docsite-preview ready!

Name	Link
🔨 Latest commit	f3e3292
🔍 Latest deploy log	https://app.netlify.com/sites/docsite-preview/deploys/65407864ad19a100084bb306
😎 Deploy Preview	https://deploy-preview-8399--docsite-preview.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.