Added CLIENT LIST iterator alternative

[vladvildanov]

Description of change

Closes #4326

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---

Note

Low Risk
Additive API with unchanged default client_list() behavior; cluster pipeline blocking mirrors existing CLIENT LIST restrictions.

Overview
Adds client_list_iter(), a streaming alternative to client_list() that yields one parsed client record at a time instead of building a full list[dict]. Callers with very large connection counts can process results without holding every parsed record in memory at once (the full wire reply is still read before iteration).

The response parser gains an as_iter=True path via _client_list_iter, which scans newline boundaries lazily and avoids splitlines() so line lists are not retained for the generator lifetime. Sync and async clients expose the same TYPE / ID filters as client_list().

client_list_iter is explicitly blocked on cluster pipelines (sync and async), matching CLIENT LIST behavior so it cannot be queued as a normal pipelined command.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-14T12:51:32.644409Z	2c889e2	New commits

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