Set non-zero exit code on errors

[kraenhansen]

Merging this PR will:

• Ensure the Ferric build tool fails with a non-zero exit code on usage and spawn errors.

[changeset-bot]

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Latest commit: cfb7b30

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[Copilot]

Pull Request Overview

This PR updates the Ferric build tool to set a non-zero exit code when an error occurs during command execution.

• Adds process.exitCode = 1 in the error handler to signal failure.
• Retains existing behavior for flushing spawn errors.