feat: launch core service from envar

[jonahrb]

Description

Allow the option to define ANSYS_GEOMETRY_SERVICE_ROOT envar to provide path to CoreService executable instead of assuming the unified install.

Issue linked

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)

[jonahrb]

@RobPasMue i will defer to you here. I have no experience with the launcher code so i just did what was minimally invasive and functional.

[codecov]

Codecov Report

Attention: Patch coverage is 21.73913% with 18 lines in your changes missing coverage. Please review.

Project coverage is 90.94%. Comparing base (a28172c) to head (2dac111).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ansys/geometry/core/connection/product_instance.py	21.73%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1716      +/-   ##
==========================================
- Coverage   91.03%   90.94%   -0.09%     
==========================================
  Files          91       91              
  Lines        7995     8006      +11     
==========================================
+ Hits         7278     7281       +3     
- Misses        717      725       +8     

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[RobPasMue]

Implementation looks good but we should document this somewhere - probably in the docs page where we are showing how to launch the services. Would you mind adding it there @jonahrb? Apart from that, all good - I'll approve once the docs are up.

[RobPasMue]

Need to do a local mod... I'll ping you asap