Expose Storage.data_ptr() as public API

Change the access modifier of Storage.data_ptr() from protected to public,
allowing external consumers to obtain the raw data pointer for interop with
other native libraries (e.g. bitsandbytes).

Fixes #1454

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: alinpahontu2912

src/TorchSharp/Tensor/Storage.cs

@@ -139,7 +139,7 @@ protected static Tensor CreateTypedTensor<T>(ScalarType dtype, IList<T> rawArray
             /// A pointer to the raw data in memory.
             /// </summary>
             /// <returns></returns>
-            protected IntPtr data_ptr()
+            public IntPtr data_ptr()
             {
                 if (_tensor_data_ptr != IntPtr.Zero)
                     return _tensor_data_ptr;

test/TorchSharpTest/TestTorchTensor.cs

@@ -8078,6 +8078,20 @@ public void Storage_Copy()
             Assert.Equal(data, x.data<long>().ToArray());
         }
 
+        [Fact]
+        [TestOf(nameof(Tensor.storage))]
+        public void Storage_DataPtr()
+        {
+            var data = new float[] { 1.0f, 2.0f, 3.0f, 4.0f };
+            var x = torch.tensor(data);
+
+            var st = x.storage<float>();
+            Assert.NotNull(st);
+
+            var ptr = st.data_ptr();
+            Assert.NotEqual(IntPtr.Zero, ptr);
+        }
+
         [Fact]
         [TestOf(nameof(torch.stft))]
         public void Float32STFT()