fix: update ensure_expr to reject non-Expr values for consistency

Author: kosiew

python/datafusion/expr.py

@@ -222,15 +222,15 @@
 ]
 
 
-def ensure_expr(value: Expr) -> expr_internal.Expr:
+def ensure_expr(value: Expr | Any) -> expr_internal.Expr:
     """Return the internal expression from ``Expr`` or raise ``TypeError``.
 
-    This helper rejects plain strings so higher level APIs consistently
-    require explicit :func:`~datafusion.col` or :func:`~datafusion.lit`
-    expressions.
+    This helper rejects plain strings and other non-:class:`Expr` values so
+    higher level APIs consistently require explicit :func:`~datafusion.col` or
+    :func:`~datafusion.lit` expressions.
 
     Args:
-        value: Candidate expression.
+        value: Candidate expression or other object.
 
     Returns:
         The internal expression representation.