[Android] Migrate to FlutterPlugin and ActivityAware (remove deprecated Registrar)

[MAM606]

📌 Summary

This Pull Request migrates the Android implementation of flutter_tts away from the deprecated PluginRegistry.Registrar API to the modern FlutterPlugin and ActivityAware APIs.

✅ What Changed

• Removed deprecated Registrar-based registration.
• Added FlutterPlugin onAttachedToEngine() binding.
• Implemented ActivityAware for safer context handling.
• Maintained backward compatibility with existing usage.

🧪 Testing

• ✅ Verified speaking, pitch, and rate adjustments
• ✅ Tested on Android physical device (API 33)

📎 Related Issue

Closes #592 Issue

---

Happy to adjust or expand based on feedback. Thank you for maintaining this plugin!

[echogit]

Are the comments in arabic? Wouldn't english be more broadly understood?

[MAM606]

I become more comfortable with Arabic, and I can describe my codes better in this way, thank you for your feedback. (;

[echogit]

I become more comfortable with Arabic, and I can describe my codes better in this way, thank you for your feedback. (;

I suggest using AI to translate :P

[dlutton]

@MAM606 please update the comments to English and I'll merge this in