fix(redis): replace KEYS with SCAN for better performance

[hkdeman]

Replace Redis KEYS command with SCAN to improve performance on large datasets.

The KEYS command can block the Redis server when dealing with many keys, while SCAN provides cursor-based iteration that is non-blocking.

Fixes #618

Generated with Claude Code

[jazzberry-ai]

Bug Report

Name	Severity	Example test case	Description
Race condition during SCAN	Medium	Modify keys (add/delete) in Redis while the GetStorageUnits function is running.	The SCAN command, while non-blocking, can return inconsistent results if keys are added or removed during the scan. This can lead to missing or duplicate keys in the returned list of storage units. The patch doesn't address this race condition.

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