feat: prioritize user-defined SPACECLAIM_MODE env var

[RobPasMue]

Description

Prioritize the value of env var SPACECLAIM_MODE defined by the user, to the one defined by the library.

Issue linked

Closes #1439

Checklist

• I have tested my changes locally.
• I have added necessary documentation or updated existing documentation.
• I have followed the coding style guidelines of this project.
• I have added appropriate unit tests.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have added the minimum version decorator to any new backend method implemented.
• I have made sure that the title of my PR follows Conventional commits style (e.g. feat: extrude circle to cylinder)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 91.83%. Comparing base (c84a39b) to head (74d45ff).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ansys/geometry/core/connection/product_instance.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1440      +/-   ##
==========================================
- Coverage   91.85%   91.83%   -0.03%     
==========================================
  Files          86       86              
  Lines        6878     6880       +2     
==========================================
  Hits         6318     6318              
- Misses        560      562       +2     

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