feat: add full attnres vision backbone

tests/test_attnres_resnet2d_backbone.py

@@ -0,0 +1,26 @@
+import unittest
+
+import torch
+
+
+class AttnResResNet2DBackboneTest(unittest.TestCase):
+    def test_backbone_preserves_resnet_like_stage_contract(self):
+        from roboimi.vla.models.backbones.attnres_resnet2d import AttnResResNetLikeBackbone2D
+
+        backbone = AttnResResNetLikeBackbone2D(
+            input_channels=3,
+            stem_dim=16,
+            stage_dims=(16, 32, 64, 128),
+            stage_depths=(1, 1, 1, 1),
+            stage_heads=(2, 4, 4, 8),
+            stage_kv_heads=(1, 1, 1, 1),
+            stage_window_sizes=(7, 7, 7, 7),
+            dropout=0.0,
+        )
+        x = torch.randn(2, 3, 56, 56)
+        y = backbone(x)
+        self.assertEqual(y.shape, (2, 128, 2, 2))
+
+
+if __name__ == '__main__':
+    unittest.main()