chore: flatten src/ to root

utils/withResolvers.ts

@@ -0,0 +1,13 @@
+/**
+ * Polyfill for Promise.withResolvers() (ES2024, Node 22+).
+ * package.json declares "engines": { "node": ">=18.0.0" } so we can't use the native one.
+ */
+export function withResolvers<T>(): PromiseWithResolvers<T> {
+  let resolve!: (value: T | PromiseLike<T>) => void
+  let reject!: (reason?: unknown) => void
+  const promise = new Promise<T>((res, rej) => {
+    resolve = res
+    reject = rej
+  })
+  return { promise, resolve, reject }
+}