Test: forbid np.sin out= on Expr/Variable

Add a unit test in tests/test_expr.py to assert that calling np.sin with an out= parameter on a Variable/Expr/GenExpr raises TypeError. This prevents in-place modification of expression objects via NumPy ufunc out arguments and documents the intended behavior.

Author: Zeroto521

tests/test_expr.py

@@ -272,6 +272,10 @@ def test_unary(model):
     with pytest.raises(TypeError):
         np.arcsin(x)
 
+    with pytest.raises(TypeError):
+        # forbid modifying Variable/Expr/GenExpr in-place via out parameter
+        np.sin(x, out=np.array([0]))
+
 
 def test_mul():
     m = Model()