mod(element): introduce deinit interface for deinitializing Elements automatically with the Container

src/container.zig

@@ -648,6 +648,7 @@ pub fn Container(Model: type, Event: type) type {
         pub fn deinit(this: *@This()) void {
             for (this.elements.items) |*element| element.deinit();
             this.elements.deinit(this.allocator);
+            this.element.deinit();
         }
 
         pub fn append(this: *@This(), element: @This()) !void {