Use `None` to retrieve all metric values

[kzscisoft]

Retrieve all metric values by default

Issue: Closes #548

Python Version(s) Tested: 3.13.0

Operating System(s): Ubuntu 24.10

📝 Summary

Client.get_metric_values(...) will now return all points if max_points = None or is unspecified.

🔄 Changes

Updated default to be None and not -1

✔️ Checklist

• [ ] Unit and integration tests passing.
• [ ] Pre-commit hooks passing.
• [ ] Quality checks passing.