Stop put from failing when input is an Item

src/skore/item/__init__.py

@@ -18,6 +18,9 @@
 
 def object_to_item(object: Any) -> Item:
     """Transform an object into an Item."""
+    if isinstance(object, Item):
+        return object
+
     for cls in (
         PrimitiveItem,
         PandasDataFrameItem,

src/skore/project.py

@@ -52,6 +52,7 @@ def put(self, key: str, value: Any, on_error: Literal["warn", "raise"] = "warn")
             The key to associate with `value` in the Project. Must be a string.
         value : Any
             The value to associate with `key` in the Project.
+            If an `Item`, will be inserted as-is.
         on_error : "warn" or "raise", optional
             Upon error (e.g. if the key is not a string), whether to raise an error or
             to print a warning. Default is "warn".