Make macOS CI runners opt-in

[Copilot]

macOS GitHub-hosted runners are slow to provision, making them poor candidates for blocking every PR. This adds a workflow_dispatch trigger so macOS jobs can be run on demand rather than automatically.

Changes

• workflow_dispatch trigger — adds a run_macos boolean input (default: false) to the CI workflow, enabling manual opt-in runs
• test-workspace and test-workspace-features — both jobs now gate their macos-latest matrix entry behind inputs.run_macos == true; all other runners (Windows, Linux x64, Linux ARM) are unaffected

workflow_dispatch:
  inputs:
    run_macos:
      description: "Run macOS CI jobs (slow runners, opt-in)"
      type: boolean
      default: false

if: ${{ !contains(matrix.os, 'macos') || inputs.run_macos == true }}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Make macos runner optional</issue_title>
<issue_description>## Is your feature request related to a problem? Please describe.
macos runners are slower to come by on GH

Describe the solution you'd like

make macos gates optional, so they can be run once in a while

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

Provide references (if applicable)

If your feature request is related to a published algorithm/idea, please provide links to
any relevant articles or webpages.

Additional context

Add any other context or screenshots about the feature request here.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Make macos runner optional #843

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