Install psalm as dev, sync scripts updates

vendor/amphp/byte-stream/lib/OutputBuffer.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace Amp\ByteStream;
+
+use Amp\Deferred;
+use Amp\Promise;
+use Amp\Success;
+
+class OutputBuffer implements OutputStream, Promise
+{
+    /** @var Deferred */
+    private $deferred;
+
+    /** @var string */
+    private $contents = '';
+
+    /** @var bool */
+    private $closed = false;
+
+    public function __construct()
+    {
+        $this->deferred = new Deferred;
+    }
+
+    public function write(string $data): Promise
+    {
+        if ($this->closed) {
+            throw new ClosedException("The stream has already been closed.");
+        }
+
+        $this->contents .= $data;
+
+        return new Success(\strlen($data));
+    }
+
+    public function end(string $finalData = ""): Promise
+    {
+        if ($this->closed) {
+            throw new ClosedException("The stream has already been closed.");
+        }
+
+        $this->contents .= $finalData;
+        $this->closed = true;
+
+        $this->deferred->resolve($this->contents);
+        $this->contents = "";
+
+        return new Success(\strlen($finalData));
+    }
+
+    public function onResolve(callable $onResolved)
+    {
+        $this->deferred->promise()->onResolve($onResolved);
+    }
+}