Added Overlay Widget for saving state

[Tilakraj-B]

PR Description

Removed the ScaffoldMessenger and added Overlay Widget for displaying the waiting screen while saving for better UX.

Related Issues

• Related Issue #311
• Closes #311

Checklist

• [X] I have gone through the contributing guide
• [X] I have updated my branch and synced it with project main branch before making this PR
• [X] I have run the tests (flutter test) and all tests are passing

Added/updated tests?

added tests for the new components added

• [X] Yes
• [ ] No, and this is why: please replace this line with details on why tests have not been included

[animator]

@Tilakraj-B What is the source of completed.json & saving.json? Post the URLs.

[Tilakraj-B]

The source is lottiefiles.com complete.json URL : https://lottiefiles.com/animations/examination-done-cF8EOEIeFo saving.json URL : https://lottiefiles.com/animations/save-OMZ1ESz3LP

[animator]

Added comments above.

[animator]

One more comment ☝️

[animator]

Is the PR ready for review?

[Tilakraj-B]

yes, made the changes you asked.

[animator]

LGTM. Thanks 🚀