Update mainLanding.py

[madhupashish]

The updated code introduces several enhancements aimed at improving readability, maintainability, and robustness. Constants and styles, such as font names and button styles, have been moved to the top of the script for easier modification and consistency. Function names have been standardized to enhance readability. The layout definition has been refined by structuring the multiline element for better readability. Event handling has been simplified by dynamically generating the script names based on the event text, reducing repetitive code. Additionally, the robustness of the code has been increased by ensuring that the current visualizer process is properly closed before launching a new one. These improvements collectively make the code more organized and easier to manage.

[Soumya-Kushwaha]

Please avoid raising PRs without being assigned on issues. @madhupashish