Docs batch example

[musecollaboration]

Description

This PR adds a working example of using batch=True with PullSub in NATS JetStream.
It demonstrates how to access native NATS messages via msg.raw_message and perform
per‑message ack() inside a batch.

This improves the documentation by providing a real, functional example for batch
processing, which was previously missing.

Fixes: none

Type of change

• Documentation (code examples or documentation updates)

Checklist

• I have reviewed my changes
• I have updated the documentation accordingly
• My changes do not introduce any warnings

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[musecollaboration]

Исправил