Added an example to dynamically alter the scene in each frame

[IgorTatarnikov]

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Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?
See https://forum.image.sc/t/brainrender-animation-of-slices/100612

What does this PR do?
Adds a new flag to make_video to fix the camera to the perspective of the first frame. Otherwise, if the root mesh is sliced throughout the animation the perspective will shift as the centre of mass of the root volume shifts.

Passes the callback function to subsequent frames after the last frame.

Adds an example for how to use a callback function to dynamically alter the scene throughout the Animation.

How has this PR been tested?

All tests pass locally.

Is this a breaking change?

No, the new flag is optional and the default provides the previous behaviour.

Does this PR require an update to the documentation?

Yes, will come in subsequent PR.

Checklist:

• The code has been tested locally
• Tests have been added to cover all new functionality (unit & integration)
• The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit

[codecov]

Codecov Report

Attention: Patch coverage is 20.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 86.62%. Comparing base (242dad8) to head (c0bd5e6).
Report is 1 commits behind head on main.

Files	Patch %	Lines
brainrender/video.py	20.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #376      +/-   ##
==========================================
- Coverage   88.06%   86.62%   -1.44%     
==========================================
  Files          27       27              
  Lines        1215     1219       +4     
==========================================
- Hits         1070     1056      -14     
- Misses        145      163      +18     

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[alessandrofelder]

Looks good, tiny comment about documenting arguments.