Update doctest client with latest v4 release (#2844)

packages/client/lib/errors.ts

@@ -1,3 +1,5 @@
+import { RedisCommandRawReply } from './commands';
+
 export class AbortError extends Error {
     constructor() {
         super('The command was aborted');
@@ -63,3 +65,20 @@ export class ErrorReply extends Error {
         this.stack = undefined;
     }
 }
+
+export class MultiErrorReply extends ErrorReply {
+    replies;
+    errorIndexes;
+
+    constructor(replies: Array<RedisCommandRawReply | ErrorReply>, errorIndexes: Array<number>) {
+        super(`${errorIndexes.length} commands failed, see .replies and .errorIndexes for more information`);
+        this.replies = replies;
+        this.errorIndexes = errorIndexes;
+    }
+
+    *errors() {
+        for (const index of this.errorIndexes) {
+            yield this.replies[index];
+        }
+    }
+}