Add LOS halo sampling module with negative kappa sheets

Implements line-of-sight dark matter halo sampling following He et al. (2022,
MNRAS 511, 3046). The LOSSampler class orchestrates plane slicing, halo mass/
position/concentration sampling, NFWTruncatedSph conversion, and compensatory
negative convergence sheet computation for mass conservation in multi-plane
ray-tracing simulations.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 2 people