Fix numpy 2.x compatibility: replace np.math.factorial with math.factorial

[exopoiesis]

Summary

numpy.math was deprecated in numpy 1.25 and removed in numpy 2.0 (release notes).

This causes AttributeError: module 'numpy' has no attribute 'math' when using any checkpoint that triggers GemNetTCtrl with condition_on_adapt — specifically in basis_utils.py:sph_harm_prefactor() and associated_legendre_polynomials().

Fix

Replace np.math.factorial with math.factorial from the standard library (identical behavior, zero additional dependencies). 4 occurrences in 1 file.

Affected checkpoints

Broken (with numpy >= 2.0): space_group, dft_band_gap, dft_mag_density, ml_bulk_modulus, dft_mag_density_hhi_score

Unaffected (don't trigger the code path): chemical_system, chemical_system_energy_above_hull

Reproduction

from mattergen.generator import CrystalGenerator
from mattergen.common.utils.data_classes import MatterGenCheckpointInfo

info = MatterGenCheckpointInfo.from_hf_hub("space_group")
gen = CrystalGenerator(checkpoint_info=info, batch_size=1, num_batches=1,
                        properties_to_condition_on={"space_group": 225})
gen.generate()  # → AttributeError: module 'numpy' has no attribute 'math'

Verified

Generated 192 structures with space_group checkpoint after applying this fix (RTX 4070, numpy 2.1.3, PyTorch 2.4.1).

🤖 Generated with Claude Code