Adding return types for the RedisModuleCommands class

[petyaslavova]

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Description of change

Fixes issue #3583

[Copilot]

Pull Request Overview

This PR adds return type annotations to the methods of the RedisModuleCommands class and its asynchronous subclass, clarifying the API contracts for accessing various Redis module namespaces.

• Added return type hints for methods such as json, ft, ts, bf, cf, cms, topk, tdigest, and vset.
• Updated AsyncRedisModuleCommands.ft to return an AsyncSearch instance.