Improve desktop launch

[Alberto-DM]

AEDT process would block GRPC communication with the main thread when AEDT is busy.
This fix in desktop launch method solves this problem.
Other changes in this PR:

• normalize_vector now support null vector [0,0,0]
• import_nastran improvements for speed
• removed unnecessary operation with units in add_variation

[ansys-reviewer-bot]

Thanks for opening a Pull Request. If you want to perform a review write a comment saying:

@ansys-reviewer-bot review

[codecov]

Codecov Report

Merging #3947 (cdbcf37) into main (3376ce9) will increase coverage by 0.00%.
The diff coverage is 91.66%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3947   +/-   ##
=======================================
  Coverage   81.34%   81.35%           
=======================================
  Files         182      182           
  Lines       63143    63147    +4     
=======================================
+ Hits        51366    51375    +9     
+ Misses      11777    11772    -5