mock-aws-s3-v3: ListObjectsV2Command pagination tokens are undefined #454

Description

When using mock-aws-s3-v3 to test code that relies on S3 pagination, the mock does not return ContinuationToken or NextContinuationToken for ListObjectsV2Command responses. As a result, any logic that depends on paginated listings cannot be tested using this library.

According to AWS S3 behavior, when the number of returned objects exceeds MaxKeys, the response should include:

• IsTruncated: true
• NextContinuationToken: "[token]"
• and should accept ContinuationToken in the next request

The mock currently returns the full object list with no pagination, and both tokens remain undefined.

Steps to reproduce

import { S3Client, ListObjectsV2Command } from "@aws-sdk/client-s3";
import { mockClient } from "mock-aws-s3-v3";

const mock = mockClient(S3Client);

mock.on(ListObjectsV2Command).resolves({
  Contents: [...Array(200).keys()].map(i => ({ Key: `file-${i}` })),
  // Expecting pagination when > MaxKeys (default 1000 or custom)
});

const client = new S3Client({});

const res = await client.send(
  new ListObjectsV2Command({
    Bucket: "test-bucket",
    MaxKeys: 10,
  })
);

console.log(res.IsTruncated);           // expected: true  
console.log(res.NextContinuationToken); // expected: string
console.log(res.Contents.length);       // expected: 10

Actual behavior

• Returning up to MaxKeys number of objects
• But NextContinuationToken is undefined

Expected behavior

• Should return up to MaxKeys number of objects
• Should return a NextContinuationToken
• Should take an optional ContinuationToken