Add dynamic_startup_nodes parameter to async RedisCluster

[petyaslavova]

Pull Request check-list

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• Is the new or changed code fully tested?
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Description of change

This PR is a copy of PR #3447, originally implemented by @Kakadus

The async version of the RedisCluster lacked the dynamic_startup_nodes parameter. This PR adds the parameter to be activated when dynamic DNS endpoints for startup nodes are in use.

Enabling dynamic_startup_nodes fixes #2472, which describes the problem in detail.

#3111 also addresses said issue, but their logic is different to the sync version, while this approach moves the behaviour of the async version closer to the sync version.

[Copilot]

Pull Request Overview

Adds support for an optional dynamic_startup_nodes flag in the async RedisCluster client so that startup nodes can be replaced with all discovered nodes when using dynamic DNS endpoints.

• Introduces a dynamic_startup_nodes: bool = True parameter to RedisCluster.__init__ and propagates it into NodesManager.
• Updates NodesManager.initialize() to repopulate startup_nodes from all discovered nodes when the flag is true.
• Adds a new parametrized test in tests/test_asyncio/test_cluster.py to validate both dynamic and static startup node behavior.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tests/test_asyncio/test_cluster.py	Adds test_init_slots_dynamic_startup_nodes to verify startup node list based on flag.
redis/asyncio/cluster.py	Adds dynamic_startup_nodes parameter, stores it in NodesManager, and applies dynamic behavior in initialize().

Comments suppressed due to low confidence (2)

tests/test_asyncio/test_cluster.py:2741

• [nitpick] The local variable startup_nodes shadows the attribute rc.nodes_manager.startup_nodes. Consider renaming it to something like expected_nodes for clarity in the test.

startup_nodes = list(rc.nodes_manager.startup_nodes.keys())

redis/asyncio/cluster.py:1451

• There’s no test covering the behavior when initialize() is called multiple times. Consider adding a test to verify that subsequent topology refreshes still respect and enforce dynamic_startup_nodes (e.g., removing stale entries).

if self._dynamic_startup_nodes: