chore: v1 implementation of parts and commands stubs

[jacobrkerstetter]

Description

As title says
Will likely rename the parts stub as it is only a legacy export method

Issue linked

Related to #2388

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

❌ Patch coverage is 10.34483% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.62%. Comparing base (1dc6cd4) to head (d047aac).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ys/geometry/core/_grpc/_services/v1/conversions.py	9.09%	20 Missing ⚠️
...ansys/geometry/core/_grpc/_services/v1/commands.py	14.28%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2432      +/-   ##
==========================================
- Coverage   91.80%   91.62%   -0.18%     
==========================================
  Files         169      169              
  Lines       11813    11838      +25     
==========================================
+ Hits        10845    10847       +2     
- Misses        968      991      +23     

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