feat(ui): add useAssertSingleton hook

Use this to enforce singleton components and hooks.

invokeai/frontend/web/src/common/hooks/useAssertSingleton.ts

@@ -0,0 +1,18 @@
+import { useEffect } from 'react';
+import { assert } from 'tsafe';
+
+const IDS = new Set<string>();
+
+/**
+ * Asserts that there is only one instance of a singleton entity. It can be a hook or a component.
+ * @param id The ID of the singleton entity.
+ */
+export function useAssertSingleton(id: string) {
+  useEffect(() => {
+    assert(!IDS.has(id), `There should be only one instance of ${id}`);
+    IDS.add(id);
+    return () => {
+      IDS.delete(id);
+    };
+  }, [id]);
+}