Clarify GH systematic errors applied to v and sigma instead of h1 and h2

[maindlt]

• Fixed a bug that falsely assigned the errors dh1 and dh2 to dv and dsigma (affects NNLS solves).
• Minor redesign: pulled calculating dh1 and dh2 errors out of GaussHermite.get_data() and put it back into GaussHermite.get_observed_values_and_uncertainties().
• Included a check ensuring nonzero systematic errors for extra GH coefficients (i.e., if number_GH in the config file is bigger than the number of GH coefficients in the data).

Tested with test_nnls.py and test_notebooks.sh, to do: test on a galaxy with > 1 kinematics (FCC042?).

Closes #353 and #358.

[maindlt]

Tested successfully with FCC042 (2 kinematics sets), varying weight solvers (LegacyWeightSolver and NNLS), this pull request ("PR"), current master branch ("MB"), master branch before implementing arbitrary numbers of GH coefficients were possible ("MB pre-number-GH-fix"). Data see below.

Will merge as discussed ;-)

LegacyWeightSolver, PR
       m-bh         a-bh c-dh   f-dh  q-stars p-stars u-stars  ml        chi2             kinchi2          kinmapchi2     
------------------ ----- ---- ------- ------- ------- ------- --- ------------------ ----------------- ------------------ 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 5.5 424493.15420013765 65666.78023535715 113735.67888008912 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 4.5  429197.1525016983 67539.82992857283  87613.20983329182 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 6.5  429339.9158990041 71949.22739494297 164348.79223217713 

NNLS, PR
       m-bh         a-bh c-dh   f-dh  q-stars p-stars u-stars  ml        chi2             kinchi2          kinmapchi2     
------------------ ----- ---- ------- ------- ------- ------- --- ------------------ ----------------- ------------------ 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 5.5 424493.15420013946 65666.78023530384 113735.67911982398 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 4.5  429197.1525017018 67539.82992860806  87613.20968621966 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 6.5 429339.91589900514 71949.22739492588 164348.79271744133 

LegacyWeightSolver, MB
       m-bh         a-bh c-dh   f-dh  q-stars p-stars u-stars  ml        chi2             kinchi2          kinmapchi2     
------------------ ----- ---- ------- ------- ------- ------- --- ------------------ ----------------- ------------------ 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 5.5 424493.15420013765 65666.78023535715 113735.67888008912 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 4.5  429197.1525016983 67539.82992857283  87613.20983329182 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 6.5  429339.9158990041 71949.22739494297 164348.79223217713 

NNLS, MB
       m-bh         a-bh c-dh   f-dh  q-stars p-stars u-stars  ml        chi2             kinchi2          kinmapchi2     
------------------ ----- ---- ------- ------- ------- ------- --- ------------------ ----------------- ------------------ 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 5.5 424493.15420013946 65666.78023530384 113735.67911982398 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 4.5  429197.1525017018 67539.82992860806  87613.20968621966 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 6.5 429339.91589900514 71949.22739492588 164348.79271744133 

LegacyWeightSolver, MB pre-number-GH-fix (as of commit d4aa5c7, 3 Nov, 2023)
       m-bh         a-bh c-dh   f-dh  q-stars p-stars u-stars  ml        chi2             kinchi2          kinmapchi2     
------------------ ----- ---- ------- ------- ------- ------- --- ------------------ ----------------- ------------------ 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 5.5 424493.15420013765 65666.78023535715 113735.67888008912 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 4.5  429197.1525016983 67539.82992857283  87613.20983329182 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 6.5  429339.9158990041 71949.22739494297 164348.79223217713 

NNLS, MB pre-number-GH-fix (as of commit d4aa5c7, 3 Nov, 2023)
       m-bh         a-bh c-dh   f-dh  q-stars p-stars u-stars  ml        chi2             kinchi2          kinmapchi2     
------------------ ----- ---- ------- ------- ------- ------- --- ------------------ ----------------- ------------------ 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 5.5 424493.15420013946 65666.78023530384 113735.67911982398 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 4.5  429197.1525017018 67539.82992860806  87613.20968621966 
3162277.6601683795 0.001 10.0 1.25893     0.2     0.7  0.9999 6.5 429339.91589900514 71949.22739492588 164348.79271744133