Add CurveFitter with scipy least_squares, configurable loss functions
(soft_l1, huber, cauchy), profile likelihood, confidence intervals, and
goodness-of-fit metrics. Add CWExtractor for extracting shape factors
from beta spectra via Kurie analysis, parametrization fitting, and
g_V/g_A extraction. Includes 32 new tests (18 fitter + 14 CW extractor).
Bump version to 0.3.0.
Implemented all planned corrections:
- finite-size e/m L0 and U
- atomic screening and exchange
- radiative (electron only so far)
Added plotter and csv_export
Add implementation for the basic set of spectrum components:
Primary
-------
- Phase Space
- Fermi Function
Corrections
-----------
- Atomic:
- Screening
- Atomic exchange
- E/M and finite size:
- Finite nucleus size and charge distribution
- Radiative