docs: use context manager in read session examples

[quettabit]

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[quettabit]

@greptileai review pls

[greptile-apps]

Greptile Summary

This PR updates read-session examples to use explicit async context management. The main changes are:

• Wraps the consumer read session in async with.
• Updates five documentation examples to iterate over the entered session.
• Ensures read sessions close when each context exits.

Confidence Score: 5/5

This looks safe to merge.

• The examples follow the supported async context-manager and iterator contracts.
• Context exit closes the session and stops its background read task.
• No blocking issues were found in the updated code.

Important Files Changed

Filename	Overview
examples/consumer.py	Uses the read session as an async context manager before iterating over batches.
examples/docs/streams.py	Updates the documented read-session variants to use explicit context-managed cleanup.

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