rethinking design of tensor.

lib/src/splat/tensor.dart

@@ -5,6 +5,10 @@ import 'package:collection/collection.dart';
 class Tensor extends DelegatingList<DelegatingList<double>> {
   Tensor(super.base);
 
+  factory Tensor.fromList(List<List<double>> lst) {
+    return Tensor(DelegatingList(lst.map((e) => DelegatingList(e)).toList()));
+  }
+
   Tensor each(Function(double, int, int) f) {
     Tensor other = Tensor([]);
     for (int j = 0; j < length; ++j) {

lib/src/test/splat/tensor_test.dart

@@ -17,6 +17,20 @@ void main() {
       ]));
 
       expect(Tensor.stack(x)[0], equals(x));
+      expect(
+          Tensor.stack(x),
+          equals(Tensor.fromList([
+            [
+              [
+                [0.3367, 0.1288, 0.2345],
+                [0.3367, 0.1288, 0.2345],
+              ],
+              [
+                [0.2303, -1.1229, -0.1863],
+                [0.2303, -1.1229, -0.1863]
+              ]
+            ]
+          ])));
     });
   });
 }