Correct for sample absorption in cylindrical powder diffraction

[AndrewSazonov]

Powder samples in a cylindrical (Debye–Scherrer) holder absorb the beam by an amount that varies with scattering angle, slightly distorting the measured peak intensities. EasyDiffraction can now model this: switch it on with experiment.absorption.type = 'cylinder-hewat' and set the sample's mu_r (absorption coefficient × radius).

The correction is applied consistently for both the CrysPy and CrysFML calculation engines and reproduces FullProf's cylindrical correction to four decimal places, removing an intensity mismatch of several percent for absorbing samples — demonstrated on the LaB₆ reference at μR = 0.7, where enabling the correction brings the calculated pattern into agreement with FullProf. Values beyond the validated range are still calculated but now raise a clear warning instead of failing silently.

Time-of-flight and flat-plate geometries are designed for but not yet enabled.

[codecov]

Codecov Report

❌ Patch coverage is 93.63057% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.46%. Comparing base (bfa1f08) to head (0f50238).

Files with missing lines	Patch %	Lines
...easydiffraction/datablocks/experiment/item/base.py	86.36%	2 Missing and 1 partial ⚠️
...asydiffraction/datablocks/experiment/item/enums.py	75.00%	2 Missing and 1 partial ⚠️
src/easydiffraction/io/cif/iucr_writer.py	50.00%	1 Missing and 1 partial ⚠️
...atablocks/experiment/categories/absorption/base.py	96.15%	1 Missing ⚠️
...diffraction/datablocks/experiment/item/bragg_pd.py	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #202      +/-   ##
===========================================
+ Coverage    90.30%   90.46%   +0.16%     
===========================================
  Files          274      280       +6     
  Lines        23380    23535     +155     
  Branches      2727     2742      +15     
===========================================
+ Hits         21113    21291     +178     
+ Misses        1693     1664      -29     
- Partials       574      580       +6     

Flag	Coverage Δ
unittests	90.46% <93.63%> (+0.16%)	⬆️

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

Files with missing lines	Coverage Δ
...easydiffraction/analysis/calculators/absorption.py	100.00% <100.00%> (ø)
...rc/easydiffraction/analysis/calculators/crysfml.py	49.00% <100.00%> (+8.59%)	⬆️
src/easydiffraction/analysis/calculators/cryspy.py	49.65% <100.00%> (+4.37%)	⬆️
...locks/experiment/categories/absorption/__init__.py	100.00% <100.00%> (ø)
...experiment/categories/absorption/cylinder_hewat.py	100.00% <100.00%> (ø)
...blocks/experiment/categories/absorption/factory.py	100.00% <100.00%> (ø)
...atablocks/experiment/categories/absorption/none.py	100.00% <100.00%> (ø)
...atablocks/experiment/categories/absorption/base.py	96.15% <96.15%> (ø)
...diffraction/datablocks/experiment/item/bragg_pd.py	94.56% <87.50%> (-0.68%)	⬇️
src/easydiffraction/io/cif/iucr_writer.py	96.23% <50.00%> (-0.29%)	⬇️
... and 2 more

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