[bugfix] - fix L1/L2 scaling: move regularisation out of grad_compute into state_adjust

Regularisation terms (L1, L2, weight_decay) were being divided by mini_batch_size
in state_adjust along with the CD gradient. The CD gradient is a batch sum so
1/N normalisation is correct; regularisation penalties are per-weight and
batch-size independent. Separating them makes l1_lambda/l2_lambda directly
interpretable regardless of batch size.

Also adds --l1_lambda CLI arg to test_faces_sub_image.py and sets num_epochs=1000.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/tests/test_faces_sub_image.py

@@ -14,17 +14,18 @@ STRIDE    = 16    # 50% overlap; set equal to PATCH for non-overlapping
 GRAYSCALE = False  # reassigned in __main__ when --grayscale is set
 N_CH      = 1 if GRAYSCALE else 3
 N_VIS     = N_CH * PATCH * PATCH   # 1024 grayscale / 3072 colour
-N_HID     = 64
+N_HID     = 128
 N_IMAGES  = 50
 
 
 class TestModel(Model):
-	def __init__(self, name: str, work_dir: str = '.'):
+	def __init__(self, name: str, work_dir: str = '.', l1_lambda: float = 0.0):
 		super().__init__(name, work_dir)
 		self.unit1 = Entity(
 			(N_VIS, N_HID),
 			EntityParams(do_gaussian_visible=True, do_gaussian_hidden=False),
-			TrainingParams(learning_rate=0.001, momentum=0.9, num_epochs=3000, mini_batch_size=1000)
+			TrainingParams(learning_rate=0.001, momentum=0.9, num_epochs=1000, mini_batch_size=1000,
+			               l1_lambda=l1_lambda)
 		)
 
 	def forward(self, x: Mat) -> Mat:
@@ -175,6 +176,8 @@ if __name__ == '__main__':
 	                help='Train the model (default: false)')
 	ap.add_argument('--grayscale',  action='store_true', default=False,
 	                help='Use single-channel grayscale patches (default: false)')
+	ap.add_argument('--l1_lambda',  type=float, default=0.0,
+	                help='L1 regularisation strength (default: 0.0)')
 	args = ap.parse_args()
 
 	if args.grayscale:
@@ -185,7 +188,7 @@ if __name__ == '__main__':
 	prj_name = 'faces_sub_image_gray' if args.grayscale else 'faces_sub_image'
 	work_dir = 'results'
 
-	model = TestModel(prj_name, work_dir)
+	model = TestModel(prj_name, work_dir, l1_lambda=args.l1_lambda)
 	model.init(0.001)
 
 	if args.load_model: