Allow stackup thickness and area weight to be None

[greschd]

When the fabrics in a stackup do have a material, or the stackup has no fabrics, the 'thickness' and 'area_weight' properties cannot be computed. This change allows these properties to be 'None' in these cases.

This case is only supported in the 26.1 server version or later. Earlier versions would raise an error when getting the properties under these conditions.

Depends on ansys/ansys-api-acp#85

TODO: release the API change, update pyproject.toml and poetry.lock.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.46%. Comparing base (b5371f5) to head (e001916).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #873      +/-   ##
==========================================
- Coverage   94.88%   90.46%   -4.42%     
==========================================
  Files         110      110              
  Lines        5842     5842              
  Branches      339        0     -339     
==========================================
- Hits         5543     5285     -258     
- Misses        298      557     +259     
+ Partials        1        0       -1     

Flag	Coverage Δ
direct-launch	?
minimum-deps	?
python-3.10	?
python-3.11	?
python-3.12	?
python-3.13	90.46% <100.00%> (-3.79%)	⬇️
server-2024R2	90.46% <100.00%> (ø)
server-2025R1	?
server-2025R2	?
server-2026R1	?
server-latest	?

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