Hitless-Upgrade: Add handling of MOVING push notification with "null" host:port info.

[petyaslavova]

Pull Request check-list

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• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?

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Description of change

Adding handling for the cases when push notification doesn't contain new host and port pair - it just contains "null" txt.
For this case we are not supposed to reconnect immediately - we should wait half of the ttl in the notification and then trigger reconnects to the originally set host address.

[Copilot]

Pull Request Overview

This PR adds support for handling MOVING push notifications that contain "null" host:port information instead of actual host and port values. The key changes implement a delayed reconnection strategy where the client waits for half the TTL before triggering reconnects to the originally configured host address.

• Added handling for MOVING events with null host/port values
• Implemented delayed reconnection logic using threading.Timer
• Enhanced connection pool update mechanisms with event hash tracking

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/test_maintenance_events_handling.py	Added comprehensive test coverage for null MOVING events and enhanced existing test validation
tests/test_maintenance_events.py	Added unit test for MOVING events with null host/port values
redis/maintenance_events.py	Implemented core logic for handling null MOVING events with delayed reconnection
redis/connection.py	Enhanced connection pool management with event hash tracking and simplified reconnection methods
redis/_parsers/base.py	Added parser support for null host/port values in MOVING notifications

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