[3.9-TS] Expand Test Coverage with End-to-End and Visual Regression Tests: Implement E2E and visual regression tests to improve stability and quality

[sedghi]

What feature or change would you like to see made?

• Implement end-to-end (E2E) tests to validate the entire user flow and experience
• Add visual regression tests to catch any unintended visual changes or regressions

Why should we prioritize this feature?

Enhancing test coverage, particularly with E2E and visual regression tests, is crucial for improving the stability and quality of the viewer application.

[IbrahimCSAE]

cornerstonejs/cornerstone3D#1250

[james-hanks]

• Add list of test coverage once ticket is complete
• Publish guide to community so they can contribute to test writing