Downgrade CI may need adjustment for Optim extension

Issue

The Downgrade CI workflow uses julia-downgrade-compat to test against minimum compatible versions of dependencies. With the change in #244 making Optim a weak dependency (extension), the downgrade CI behavior may need adjustment.

Background

PR #244 moves Optim from [deps] to [weakdeps] with a package extension. The current Downgrade workflow in .github/workflows/Downgrade.yml uses julia-actions/julia-downgrade-compat@v2 which downgrades all dependencies to their minimum compatible versions.

Potential issues

1. The downgrade action may not properly handle weak dependencies/extensions
2. The extension tests require Optim to be loaded, but the downgrade behavior for weak deps may differ
3. The skip parameter in the workflow currently only skips Pkg,TOML

Suggested resolution

Consider one of:

• Adding Optim to the skip list in the Downgrade workflow
• Verifying that julia-downgrade-compat properly handles weak dependencies
• Updating the test targets to ensure Optim is properly loaded during downgrade tests

Related

• PR #244 - Make Optim an extension package

Start with .github/workflows/Downgrade.yml and the julia-actions/julia-downgrade-compat@v2 configuration, then review PR #244's extension changes. Verify how weak dependencies and Optim loading behave in downgrade CI, and confirm that the workflow's dependency handling and extension tests complete successfully.