Fix Excel generation (#645)

[RuggeroFabbiano]

Replace np.NaN with np.nan following change in Numpy 2.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.16%. Comparing base (d13a79a) to head (8cd4776).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #646      +/-   ##
==========================================
- Coverage   72.78%   72.16%   -0.63%     
==========================================
  Files          75       75              
  Lines       10447    10447              
==========================================
- Hits         7604     7539      -65     
- Misses       2843     2908      +65     

Flag	Coverage Δ
bdist_linux_310_python	?
bdist_linux_311_python	?
bdist_linux_312_python	?
bdist_linux_313_python	?
bdist_mac_310_python	?
bdist_mac_311_python	?
bdist_mac_312_python	?
bdist_mac_313_python	?
bdist_win_310_python	?
bdist_win_311_python	?
bdist_win_312_python	?
bdist_win_313_python	?
sdist_linux_310_python	?
sdist_linux_311_python	?
sdist_linux_312_python	?
sdist_linux_313_python	?
sdist_mac_310_python	72.02% <ø> (-0.53%)	⬇️
sdist_mac_311_python	72.04% <ø> (-0.50%)	⬇️
sdist_mac_312_python	72.04% <ø> (-0.54%)	⬇️
sdist_mac_313_python	71.95% <ø> (-0.62%)	⬇️
sdist_win_310_python	60.69% <ø> (-11.99%)	⬇️
sdist_win_311_python	?
sdist_win_312_python	?
sdist_win_313_python	?

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[paulbkoch]

Thanks @RuggeroFabbiano!