Add one-call automatic background estimation for powder patterns

[AndrewSazonov]

Adds a method that estimates a sensible point-based background directly from the measured pattern (respecting excluded regions), so users no longer have to place background points by hand.

[codecov]

Codecov Report

❌ Patch coverage is 79.67480% with 50 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.24%. Comparing base (4118ef6) to head (1caea81).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
...locks/experiment/categories/background/estimate.py	77.27%	30 Missing and 5 partials ⚠️
...tablocks/experiment/categories/background/enums.py	44.44%	10 Missing ⚠️
...s/experiment/categories/background/line_segment.py	92.64%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #193      +/-   ##
===========================================
- Coverage    80.25%   80.24%   -0.01%     
===========================================
  Files          262      263       +1     
  Lines        21961    22206     +245     
  Branches      2551     2587      +36     
===========================================
+ Hits         17624    17819     +195     
- Misses        3368     3411      +43     
- Partials       969      976       +7     

Flag	Coverage Δ
unittests	80.24% <79.67%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
src/easydiffraction/core/category.py	95.12% <100.00%> (+0.12%)	⬆️
src/easydiffraction/core/collection.py	96.47% <100.00%> (+0.08%)	⬆️
src/easydiffraction/display/tablers/pandas.py	81.96% <100.00%> (ø)
...s/experiment/categories/background/line_segment.py	92.95% <92.64%> (-0.29%)	⬇️
...tablocks/experiment/categories/background/enums.py	50.00% <44.44%> (-7.15%)	⬇️
...locks/experiment/categories/background/estimate.py	77.27% <77.27%> (ø)

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