Test batch queue messages in `@fedify/cfworkers`

[dahlia]

@fedify/cfworkers uses sendBatch() for enqueueMany(), and each batch item must keep the same wrapped message shape as single enqueue. A focused test would catch shape drift between the two paths.

Add a test in packages/cfworkers/src/mod.test.ts that verifies WorkersMessageQueue.enqueueMany() sends wrapped payloads and preserves the ordering key.

Suggested check: mise run check-each cfworkers.

[whangsg]

I'd like to work on this issue. Could you please assign it to me?

[dahlia]

@whangsg Assigned. Thanks!

[github-actions]

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