Minor tweaks to PyMechanical workflow examples

[greschd]

• Add note about why the PyMechanical shell workflow and PyMechanical to CDB workflow results are not exactly equal
• Remove TODO about material import; I think the current example code is ok
• Add some comments to Mechanical code
• Make values in CDB to PyMechanical example more reasonable

Checked manually that the results match with an equivalent workflow set up in WB.

Closes #703.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.04%. Comparing base (27b8395) to head (06e5ba9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #712   +/-   ##
=======================================
  Coverage   95.04%   95.04%           
=======================================
  Files         109      109           
  Lines        5716     5716           
  Branches      324      324           
=======================================
  Hits         5433     5433           
  Misses        282      282           
  Partials        1        1           

Flag	Coverage Δ
direct-launch	91.65% <ø> (ø)
minimum-deps	93.25% <ø> (ø)
python-3.10	94.31% <ø> (ø)
python-3.11	94.24% <ø> (ø)
python-3.12	94.43% <ø> (ø)
server-2024R2	90.88% <ø> (ø)
server-2025R1	94.24% <ø> (ø)
server-2025R2	94.24% <ø> (ø)
server-latest	94.85% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.