test(conformance): add sandbox lifecycle scenario

[elezar]

Summary

Add portable sandbox lifecycle conformance coverage on top of the candidate-installation test-guest flow in #3181.

Related Issue

No issue required: localized conformance coverage extension requested directly.

Changes

• Refactor conformance scenarios into a common execution trait with composable collections.
• Add the public sandbox-lifecycle collection with private stop/start and stopped-deletion leaves.
• Run sandbox-lifecycle immediately before sandbox-continuity in the restart conformance plan.
• Validate the lifecycle collection in the conformance plan parser.

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (scenario coverage added; target-backed execution is pending CI)
• cargo test -p openshell-conformance -p openshell-conformance-cli
• cargo clippy -p openshell-conformance -p openshell-conformance-cli --all-targets -- -D warnings

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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[elezar]

/ok to test