Added a very complicated AsyncIterableReader class.

The class was already implemented in
"https://deno.land/std@0.144.0/streams/conversion.ts".  So, I litterally
lost 1 day of work!  I hate myself.

vendor/deno.land/std@0.188.0/io/multi_reader.ts

@@ -0,0 +1,25 @@
+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+// This module is browser compatible.
+
+import type { Reader } from "../types.d.ts";
+
+/** Reader utility for combining multiple readers */
+export class MultiReader implements Reader {
+  readonly #readers: Reader[];
+  #currentIndex = 0;
+
+  constructor(readers: Reader[]) {
+    this.#readers = [...readers];
+  }
+
+  async read(p: Uint8Array): Promise<number | null> {
+    const r = this.#readers[this.#currentIndex];
+    if (!r) return null;
+    const result = await r.read(p);
+    if (result === null) {
+      this.#currentIndex++;
+      return 0;
+    }
+    return result;
+  }
+}