Add --smear-function option and Lorentzian smearing

[Sparks29032]

Addresses part of #211. This adds a Lorentzian smearing option.

We will need another PR that allows the user to pass a general smearing function, but the outline for how to do that is already done in this PR and should be relatively straightforward to implement from here.

The default if --smear-function is not enabled is still Gaussian, no no workflow changes will have to be made for those using the Gaussian smearing.

Below are two morphs. The morphed function is a Lorentzian with HWHM 0.1. The target is a Lorentzian with HWHM 0.25. The first image is when Gaussian smearing (and scaling) is applied. The second is when Lorentzian smearing (and scaling) is applied.

Gaussian smearing:

Lorentzian smearing:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.93%. Comparing base (9981f82) to head (a2d64ae).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #309   +/-   ##
=======================================
  Coverage   99.93%   99.93%           
=======================================
  Files          24       24           
  Lines        1570     1624   +54     
=======================================
+ Hits         1569     1623   +54     
  Misses          1        1           

Files with missing lines	Coverage Δ
tests/test_morph_func.py	100.00% <100.00%> (ø)
tests/test_morphapp.py	100.00% <100.00%> (ø)
tests/test_morphio.py	100.00% <100.00%> (ø)
tests/test_morphsmear.py	100.00% <100.00%> (ø)
tests/test_refine.py	100.00% <ø> (ø)

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[sbillinge]

one small gripe, but a great PR, thanks!

[sbillinge]

per group standard, please specify what the expected behavior is for each case, something like
# Test Gaussian default. Expect Gaussian convolution is correctly applied

[sbillinge]

see above and for all the cases

[Sparks29032]

@sbillinge Updated headers. Tests for the i/o are in test_morphio.py and only check if the file headers produced are correct and that the new option is handled correctly. No morphs are applied (apply=True with smear=0 in those tests). The actual test for the Lorentzian morph behavior is in test_morphsmear.py.