Upgrade and modernize Ax Sweeper #3176

Motivation

The Ax Sweeper plugin has fallen behind the current Ax/Python ecosystem. Its dependency pins and Python support metadata should be updated, and the implementation should use the modern Ax API instead of deprecated service APIs.

Scope

• Upgrade the Ax Sweeper plugin to a current Ax release.
• Update plugin Python support metadata to the versions supported by the current Ax stack.
• Migrate off deprecated Ax client APIs where practical.
• Preserve support for Hydra sweep overrides including ranges, integer intervals, choices, fixed values, log-scale ranges, status quo, and outcome constraints.
• Keep or improve plugin test coverage while avoiding unnecessarily slow full-process integration tests.
• Add an appropriate plugin news fragment.

Notes

Plugins may support a narrower Python version range than Hydra core when required by their dependency stack.