add cpxmod field to eigs function in math module

[Gryfenfer97]

fix #1166
I chose not to check the value of algo to know if we can apply cpxmod in the MODOPT command as it is already handle by MAPDL, but this behavior could be changed.

[codecov]

Codecov Report

Merging #2074 (fae50f4) into main (a25fa9e) will increase coverage by 3.44%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2074      +/-   ##
==========================================
+ Coverage   82.98%   86.42%   +3.44%     
==========================================
  Files          44       45       +1     
  Lines        7932     7971      +39     
==========================================
+ Hits         6582     6889     +307     
+ Misses       1350     1082     -268     

[germa89]

I chose not to check the value of algo to know if we can apply cpxmod in the MODOPT command as it is already handle by MAPDL, but this behavior could be changed.

I agree. Most of times, MAPDL handling stuff is preferable, unless there is an incompatibility with PyMAPDL or we are really improving something on MAPDL (plottting for example). But, PyMAPDL should ALWAYS follow MAPDL guidance.

LGTM. Just a small comment.