ArithArrayContainer: add __pow__, __rpow__

Author: inducer

arraycontext/container/__init__.py

@@ -168,6 +168,8 @@ def __mul__(self, other: ArrayOrScalar | Self) -> Self: ...
     def __rmul__(self, other: ArrayOrScalar | Self) -> Self: ...
     def __truediv__(self, other: ArrayOrScalar | Self) -> Self: ...
     def __rtruediv__(self, other: ArrayOrScalar | Self) -> Self: ...
+    def __pow__(self, other: ArrayOrScalar | Self) -> Self: ...
+    def __rpow__(self, other: ArrayOrScalar | Self) -> Self: ...
 
 
 ArrayContainerT = TypeVar("ArrayContainerT", bound=ArrayContainer)