EPLB: add post-rearrangement weight invariant checks
After each expert rearrangement, verify that:
- g1_alphas[i] == a13_scale * w13_weight_scale_2[i]
- g2_alphas[i] == a2_scale * w2_weight_scale_2[i]
Also logs per-weight checksums (rank 0, every 20th layer) to
track cumulative corruption across rearrangements.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Tyler Michael Smith <tlrmchlsmth@gmail.com>
