CryoSPARC .cs test fixture (20 particles)

Source: /tigress/CRYOEM/zhonglab/rh1732/02_HRA_2025/J877/J877_particles/J877_particles_exported.cs
Description: HRA 2025 challenge exported particles (homogeneous refinement)
Original dataset: 132,329 particles, 288x288, 300kV
Subset: first 20 particles
Fields: 54 (full CTF + poses + blob + location + pick_stats)

Files:
  particles_20.cs.npy - subset of 20 particles (numpy structured array)
  reference_values.npz - expected poses and CTF from recovar's parser
  README.txt - this file
