Remove unused q_start and current_q arrays from Ensemble

[mesonepigreco]

Summary

• Remove q_start and current_q arrays from the Ensemble class — these were allocated but never actively used anywhere in the codebase.
• All prior usages were commented out after the weight-update code was refactored to use the direct uYu computation instead of the old get_gaussian_weight Fortran path.

Memory savings

For a typical simulation (N=20000, nat_sc=320, 4×4×4 supercell), this saves ~293 MB of persistent memory per ensemble — roughly 12% of the total ensemble memory footprint.

What was removed

• self.q_start = np.zeros((self.N, Nsc * 3)) — allocation in __init__
• self.current_q = np.zeros((self.N, Nsc * 3)) — allocation in __init__
• All commented-out code referencing these attributes (timing stubs, GetQ_vectors calls, old weight-update paths)

Notes

• No functional changes — no active code paths were using these attributes.
• The __DEBUG_RHO__ debug block was preserved in both locations.