docs(python): clarify "clones data" in to_numpy (#10095)

py-polars/polars/series/series.py

@@ -3635,9 +3635,18 @@ def to_numpy(
         use_pyarrow: bool = True,
     ) -> np.ndarray[Any, Any]:
         """
-        Convert this Series to numpy. This operation clones data but is completely safe.
+        Convert this Series to numpy.
 
-        If you want a zero-copy view and know what you are doing, use `.view()`.
+        This operation may clone data but is completely safe. Note that:
+
+        - data which is purely numeric AND without null values is not cloned;
+        - floating point ``nan`` values can be zero-copied;
+        - booleans can't be zero-copied.
+
+        To ensure that no data is cloned, set ``zero_copy_only=True``.
+
+        Alternatively, if you want a zero-copy view and know what you are doing,
+        use `.view()`.
 
         Parameters
         ----------