Improve zOrder Handling for Object Layer Movement

[arianizadi]

Actions before raising this issue

• I searched the existing issues and did not find anything similar.
• I read/searched the docs

Is your feature request related to a problem? Please describe.

Currently, the zOrder adjustment logic in CVAT moves objects directly to minZLayer - 1 or maxZLayer + 1, which can result in unintended jumps and out-of-bounds issues.

Describe the solution you'd like

Update zOrder logic to adjust the value based on the current z index, such as moving it forward or back by one layer.

Describe alternatives you've considered

I attempted using the current implementation, but if a mistake is made and z layers need to be changed. It is a giant headache to fix. I have to remove layers and recreate masks.

Additional context

#9063