DFA + residual-branch penalty test: seed=42, lam=0.1
  ep 0: ||h_L||=8.893e+00 ||g_2||=9.934e-04 acc=0.1152
  ep 1: ||h_L||=7.313e+02 ||g_2||=1.234e-05 eval_acc=0.3330 test_acc=0.3271
  ep 10: ||h_L||=6.932e+03 ||g_2||=2.318e-06 eval_acc=0.3467 test_acc=0.3430
  ep 20: ||h_L||=1.083e+04 ||g_2||=1.721e-06 eval_acc=0.3564 test_acc=0.3531
  ep 30: ||h_L||=1.157e+04 ||g_2||=1.634e-06 eval_acc=0.3594 test_acc=0.3486

FINAL test acc: 0.3486
Compare to:
  DFA-vanilla (3-seed mean):    0.308
  DFA-shallow (3-seed mean):    0.349
  DFA-frozen (3-seed mean):     0.349
  BP-trainable (3-seed mean):   0.609
Saved results/dfa_pen_short/dfa_pen_lam0.1_s42.json
Saved results/dfa_pen_short/dfa_pen_lam0.1_s42.pt