Sentinel scan iterator

[harshrai654]

Description

This PR implements the scanIterator method for the RedisSentinel client.
Previously, scanIterator was not exposed on the Sentinel client, limiting the ability to iterate over keys on the master node directly through the Sentinel interface. This implementation adds that capability with handling for failovers.

Issue: #2999

Changes:

• Automatic Failover Handling: If a master failover occurs during iteration, the iterator detects the MASTER_CHANGE topology event and automatically restarts the scan from the beginning on the new master. This ensures all keys are eventually covered, even if the topology changes mid-scan.
• Reset-on-Failover Strategy: Since Redis cursors are stateful and specific to a node instance, the iterator deliberately restarts from cursor 0 (the beginning) upon detecting a master failover. This guarantees data completeness but may result in duplicate keys being yielded, as documented.

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Checklist

• Does npm test pass with this change (including linting)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

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[nkaradzhov]

Hi @harshrai654, thanks for the contribution! On first glance, this looks good, gut it looks like there are some failing tests. Can you please resolve those, so we can have more thorough look on the final state of the code

[jit-ci]

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[harshrai654]

Hey @nkaradzhov I have fixed the tests. A stopped node in previous test of the describe block was causing issues in the next test which requires healthy nodes in the sentinel. Added cleaning up of nodes of frame between these two tests.