REFACTOR: Point cloud extension and tests

[ecoussoux-ansys]

Following the guidelines introduced in #6303 and as part of the contributions on #6228 :

• Refactoring of the point cloud extension to use the ExtensionCommon class (introduced in REFACTOR: Extension architecture using common class #6238 ),
• Revisiting and extending unit and system tests (including UI tests) for the extension.

Close #6366

Minimal changes are also introduced in this PR with the aim of simplifying the definition of unit tests for the "move it" extension in tests/unit/extensions/test_move_it.py.
A few comments and docstrings are also refined in files defining the template extension and the tests associated with it.

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[codecov]

Codecov Report

Attention: Patch coverage is 85.53459% with 23 lines in your changes missing coverage. Please review.

Project coverage is 85.42%. Comparing base (c08417b) to head (44335dc).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #6372    +/-   ##
========================================
  Coverage   85.42%   85.42%            
========================================
  Files         175      175            
  Lines       66390    66530   +140     
========================================
+ Hits        56714    56836   +122     
- Misses       9676     9694    +18     

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[Samuelopez-ansys]

Hi @ecoussoux-ansys great job! Please could you try to increase the coverage? I think only a few cases are missed, and we could try to reach the 100%.