partial toolbar: basic writable store approach

src/lib/util.ts

@@ -1,3 +1,10 @@
+/**
+ * MaybeGetter is a type that can either be a value of type T or a function that returns a value of type T.
+ * This is useful for cases where you might want to pass a value directly or a function that computes the
+ * value later, potentially taking advantage of reactivity.
+ */
+export type MaybeGetter<T> = T | (() => T);
+
 /**
  * Generates a unique identifier string unless an identifier is provided.
  * If a prefix is provided, it will be prepended to the identifier.