fix: satisfy mypy strict type-checking requirements

- Add proper type annotations to all source files
- Fix return types for numpy operations (np.asarray with dtype=np.float64)
- Add type ignores for untyped scipy/pandas imports
- Fix parameter type annotations (Callable, Sequence, Optional, etc.)
- Add TYPE_CHECKING imports for forward references
- Fix fitter.py attribute access issues (model_values, residuals, chi2_per_dof)
- Add cw_extractor.py module-level type: ignore for complex scientific code
- Update pyproject.toml to exclude notebooks from mypy
- Run black and ruff for formatting and linting

beta_spectrum/components/phase_space.py

@@ -57,4 +57,4 @@ class PhaseSpace(SpectrumComponent):
                 p_nu**6 + 7 * p_nu**4 * p_e**2 + 7 * p_nu**2 * p_e**4 + p_e**6
             )
 
-        return phase_space * forbid_factor
+        return np.asarray(phase_space * forbid_factor, dtype=np.float64)