KEMSystemMatrix: get_weighting_subset aliased to get_projection_subset

Hi, while reading through the KEM implementation I noticed KEMSystemMatrix sets

self.get_weighting_subset = self.system_matrix.get_projection_subset

in __init__ (projectors/shared/kem_system_matrix.py:20), but the two methods take different arguments:

• get_projection_subset(projections, subset_idx) - two arguments
• get_weighting_subset(subset_idx) - one argument

PreconditionedGradientAscent calls get_weighting_subset(subset_idx) with a single argument (in the prior, uncertainty, and BSREM paths), which would hit the two-argument get_projection_subset and raise TypeError. It also returns projections rather than the scalar weight that set_beta_scale / norm_BP_weight expect.

This looks like it would break any KEM reconstruction that uses a prior (or BSREM / uncertainty estimation). I think it should alias to self.system_matrix.get_weighting_subset. The signature mismatch reproduces locally. Let me know if I've misunderstood.

Start in projectors/shared/kem_system_matrix.py:20 and compare the delegated methods with the SystemMatrix implementation. Trace the get_weighting_subset calls from PreconditionedGradientAscent in the prior, uncertainty, and BSREM paths, then reproduce the reported call. Done means those paths no longer raise a signature error and receive the weighting value expected by set_beta_scale and norm_BP_weight.