test: add comprehensive gif-animator unit test

[Rishi2600]

Summary

This PR adds Jest unit tests for gif-animator.js, which manages animated GIF playback on the turtle canvas.

fixes: #5121

Changes

• Add test suite for GIFAnimator class initialization
• Add test suite for GIF detection and ID generation
• Add test suite for animation creation and lifecycle
• Add test suite for frame rendering and transforms
• Add test suite for position updates and cleanup

Coverage

This PR adds 51 comprehensive test cases covering:

• GIFAnimator class initialization
• GIF detection and ID generation
• animation creation and lifecycle
• frame rendering and transforms
• position updates and cleanup

Covers achieved:

• Statement - 97.75% (87/89)
• Branches - 87.5% (28/32)
• Functions - 87.5% (14/16)
• Lines - 100% (84/84)

Coverge summary -

Testing

All existing tests pass, including the CI and the new tests added.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[Rishi2600]

Hey @omsuneri if you have a moment, could you please review this and if there are any suggestions, let me know. Thanks!