Add note regarding copy behavior when moving to same device

Closes: data-apis#645

Author: kgryte

src/array_api_stubs/_draft/array_object.py

@@ -1086,8 +1086,11 @@ def to_device(
             an array with the same data and data type as ``self`` and located on the specified ``device``.
 
 
-        .. note::
-           If ``stream`` is given, the copy operation should be enqueued on the provided ``stream``; otherwise, the copy operation should be enqueued on the default stream/queue. Whether the copy is performed synchronously or asynchronously is implementation-dependent. Accordingly, if synchronization is required to guarantee data safety, this must be clearly explained in a conforming library's documentation.
+        Notes
+        -----
+
+        -   When a provided ``device`` object corresponds to the same device on which an array instance resides, implementations may choose to perform an explicit copy or return ``self``.
+        -   If ``stream`` is provided, the copy operation should be enqueued on the provided ``stream``; otherwise, the copy operation should be enqueued on the default stream/queue. Whether the copy is performed synchronously or asynchronously is implementation-dependent. Accordingly, if synchronization is required to guarantee data safety, this must be clearly explained in a conforming array library's documentation.
         """