fix(createImageSliceSynchronizer): fix imageSliceSync not getting VOLUME_NEW_IMAGE event

[Luab]

Context

#2472
createImageSliceSynchronizer uses string instead of ENUM and was missing source to listen for correct event.
Also getClosestImageId check regressed in #2485

Changes & Results

• Changed createImageSliceSynchronizer VOLUME_NEW_IMAGE string to Enum
• Added source: 'element' to createImageSliceSynchronizer
• Fixed !imageIds?.length check in getClosestImageId
• Added tests

Testing

Tests for synchronization added. (Stack to Stack, Volume to Stack, Volume to Volume, bidirectional)
I am not 100% sure about Volume to Stack and Stack to Volume expected positions.

Checklist

PR

• My Pull Request title is descriptive, accurate and follows the
  semantic-release format and guidelines.

Code

• My code has been well-documented (function documentation, inline comments,
  etc.)

Public Documentation Updates

• [] The documentation page has been updated as necessary for any public API
  additions or removals.

Tested Environment

• [] "OS: Arch Linux
• [] "Node version: v25.2.1:
• [] "Browser: Chrome Headless 101.0.4950.0 (Linux x86_64)"