Replaced zrangebylex method in the range method

[cheesecake100201]

What does this PR do?

In short, provide a summary of what this PR does and why. Usually, the relevant context should be present in a linked issue.

• [Currently redis as a kvstore is bugged, as the range method uses zrangebylex method. zrangebylex method is used when it is a sorted set but we are storing the value using .set method in the redis. This causes an error. Another issue is that zrangebylex method takes 3 args but only 2 are mentioned in the range method. This causes a runtime error. That method has been replaced with the current implementation in the PR ] Addresses issue (#520 )

Test Plan

Please describe:

• tests you ran to verify your changes with result summaries.
• provide instructions so it can be reproduced. python llama_stack/apis/agents/client.py localhost 8001 tools_llama_3_1 meta-llama/Llama-3.1-70B-Instruct

Have used redis in the run.yaml file as well for the persistence_store. Also enable_session_persistence turned to True for this test. Have also tested this in a jupyter notebook to make sure the current flow does not work through multiple turns in the same session.

Sources

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Before submitting

• [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• [x] Ran pre-commit to handle lint / formatting issues.
• [x] Read the contributor guideline, Pull Request section?
• [ ] Updated relevant documentation.
• [ ] Wrote necessary unit or integration tests.