Add X-ray polarization and monochromator optics for constant-wavelength powder

[AndrewSazonov]

Constant-wavelength X-ray powder experiments now expose two incident-beam optics parameters — a polarization coefficient and a pre-specimen monochromator angle — that control the Lorentz-polarization correction applied to calculated intensities. The settings appear only on X-ray powder instruments and are honored by both the CrysPy and CrysFML engines. Neutron experiments are unaffected, and existing X-ray results stay exactly the same until you set a polarization value, so nothing changes unless you opt in.

[codecov]

Codecov Report

❌ Patch coverage is 89.79592% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.38%. Comparing base (106c84c) to head (c95c584).

Files with missing lines	Patch %	Lines
src/easydiffraction/analysis/calculators/cryspy.py	83.78%	2 Missing and 4 partials ⚠️
...sydiffraction/analysis/calculators/polarization.py	80.95%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #210      +/-   ##
===========================================
- Coverage    90.38%   90.38%   -0.01%     
===========================================
  Files          283      284       +1     
  Lines        24276    24367      +91     
  Branches      2850     2860      +10     
===========================================
+ Hits         21943    22024      +81     
- Misses        1738     1742       +4     
- Partials       595      601       +6     

Flag	Coverage Δ
unittests	90.38% <89.79%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
...rc/easydiffraction/analysis/calculators/crysfml.py	50.48% <100.00%> (+1.48%)	⬆️
...rc/easydiffraction/analysis/calculators/support.py	100.00% <ø> (ø)
...locks/experiment/categories/instrument/__init__.py	100.00% <100.00%> (ø)
...datablocks/experiment/categories/instrument/cwl.py	100.00% <100.00%> (ø)
...blocks/experiment/categories/instrument/factory.py	100.00% <100.00%> (ø)
...diffraction/datablocks/experiment/item/bragg_pd.py	94.56% <ø> (ø)
...sydiffraction/analysis/calculators/polarization.py	80.95% <80.95%> (ø)
src/easydiffraction/analysis/calculators/cryspy.py	52.15% <83.78%> (+1.98%)	⬆️

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