feat: Implement dispose method and search functionality in editor.dart

[hetsaraiya]

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• [x] I have read freeCodeCamp's contribution guidelines.
• [x] My pull request has a descriptive title (not a vague title like Update index.md)

Closes #XXXXX

This commit introduces two major changes to the editor.dart file:

1. A dispose method has been implemented to prevent memory leaks and ensure all resources are properly released when they are no longer needed.

2. Search functionality has been added to enhance the user experience by allowing users to easily find specific pieces of text within the editor.