feat(paddle): Add backward method to Paddle Frontend

ivy/functional/frontends/paddle/tensor/tensor.py

@@ -758,3 +758,11 @@ def remainder(self, y, name=None):
 
     def is_floating_point(self):
         return paddle_frontend.is_floating_point(self._ivy_array)
+
+    @with_supported_dtypes(
+        {"2.5.1 and below": ("float32", "float64", "int32", "int64")}, "paddle"
+    )
+    def backward(self, x, grad_tensor=None, retain_graph=False):
+        return paddle_frontend.Tensor.backward(
+            x, grad_tensor=grad_tensor, retain_graph=retain_graph
+        )

ivy_tests/test_ivy/test_frontends/test_paddle/test_tensor/test_tensor.py

@@ -3693,3 +3693,47 @@ def test_paddle_tensor_zero_(
         frontend=frontend,
         on_device=on_device,
     )
+
+    # backward
+@handle_frontend_method(
+    class_tree=CLASS_TREE,
+    init_tree="paddle.to_tensor",
+    method_name="backward",
+    dtype_and_x=helpers.dtype_and_values(
+        available_dtypes=helpers.get_dtypes("float"),
+    ),
+    grad_tensor=st.none()
+    | helpers.dtype_and_values(
+        available_dtypes=helpers.get_dtypes("float"),
+    ),
+    retain_graph=st.booleans(),
+)
+def test_paddle_backward(
+    dtype_and_x,
+    grad_tensor,
+    retain_graph,
+    frontend_method_data,
+    init_flags,
+    method_flags,
+    frontend,
+    on_device,
+    backend_fw,
+):
+    input_dtype, x = dtype_and_x
+
+    helpers.test_frontend_method(
+        init_input_dtypes=input_dtype,
+        init_all_as_kwargs_np={"data": x},
+        method_input_dtypes=input_dtype,
+        method_all_as_kwargs_np={
+            "grad_tensor": grad_tensor,
+            "retain_graph": retain_graph,
+            "backend_to_test": backend_fw,
+        },
+        frontend_method_data=frontend_method_data,
+        init_flags=init_flags,
+        method_flags=method_flags,
+        frontend=frontend,
+        on_device=on_device,
+    )
+