Replaced zrangebylex method in the range method (#521)

# 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`
<img width="1711" alt="Screenshot 2024-11-25 at 2 59 55 PM"
src="https://github.com/user-attachments/assets/c2551555-bc73-4427-b09b-c86d6deb2956">
<img width="634" alt="Screenshot 2024-11-25 at 3 00 33 PM"
src="https://github.com/user-attachments/assets/a087718f-fc2a-424b-b096-4ecad08a07bf">

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

Please link relevant resources if necessary.


## 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](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [ ] Wrote necessary unit or integration tests.

llama_stack/providers/utils/kvstore/redis/redis.py

@@ -48,5 +48,27 @@ async def delete(self, key: str) -> None:
     async def range(self, start_key: str, end_key: str) -> List[str]:
         start_key = self._namespaced_key(start_key)
         end_key = self._namespaced_key(end_key)
+        cursor = 0
+        pattern = start_key + "*"  # Match all keys starting with start_key prefix
+        matching_keys = []
+        while True:
+            cursor, keys = await self.redis.scan(cursor, match=pattern, count=1000)
 
-        return await self.redis.zrangebylex(start_key, end_key)
+            for key in keys:
+                key_str = key.decode("utf-8") if isinstance(key, bytes) else key
+                if start_key <= key_str <= end_key:
+                    matching_keys.append(key)
+
+            if cursor == 0:
+                break
+
+        # Then fetch all values in a single MGET call
+        if matching_keys:
+            values = await self.redis.mget(matching_keys)
+            return [
+                value.decode("utf-8") if isinstance(value, bytes) else value
+                for value in values
+                if value is not None
+            ]
+
+        return []