Upgrade kf_config.json to v2 (nested config + weight_dtype)

kf_config.json

@@ -1,31 +1,35 @@
 {
   "library_name": "kerasformers",
-  "kerasformers_version": "1.1.3",
+  "kerasformers_version": "1.2.1",
   "model_module": "kerasformers.models.nextvit",
   "model_class": "NextViTImageClassify",
   "variant": "nextvit_base_bd_in1k",
   "weights": "model.weights.h5",
+  "schema_version": 2,
+  "weight_dtype": "float32",
   "model_type": "nextvit",
-  "depths": [
-    3,
-    4,
-    20,
-    3
-  ],
-  "stem_chs": [
-    64,
-    32,
-    64
-  ],
-  "head_dim": 32,
-  "mix_block_ratio": 0.75,
-  "sr_ratios": [
-    8,
-    4,
-    2,
-    1
-  ],
-  "drop_path_rate": 0.1,
-  "image_size": 224,
-  "num_classes": 1000
+  "vision_config": {
+    "depths": [
+      3,
+      4,
+      20,
+      3
+    ],
+    "stem_chs": [
+      64,
+      32,
+      64
+    ],
+    "head_dim": 32,
+    "mix_block_ratio": 0.75,
+    "sr_ratios": [
+      8,
+      4,
+      2,
+      1
+    ],
+    "drop_path_rate": 0.1,
+    "image_size": 224,
+    "num_classes": 1000
+  }
 }