Setup test coverage with vitest

[Copilot]

• Add continue-on-error: true to the "Run tests with coverage" step so the coverage job doesn't fail when a test fails
• Add if: always() to the "Upload coverage report" step so partial coverage is still uploaded
• Add continue-on-error: true to the "Download coverage report" step in the build job so the build proceeds even if no coverage artifact exists

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[changeset-bot]

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Latest commit: 7ad263e

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