Improve Type Safety in shell.ts

[google-labs-jules]

This change refactors src/utils/shell.ts to improve type safety when handling the result of an execa command that is run with the { reject: false } option. The original code used a @ts-expect-error to suppress a type error, but this change introduces a more robust solution. By using the result.failed property as a type guard and a type assertion, TypeScript can correctly infer the ExecaError type, making the code safer and more readable.

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PR created automatically by Jules for task 5112588298335066586 started by @serhalp

[google-labs-jules]

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[github-actions]

📊 Benchmark results

Comparing with c76dbdd

• Dependency count: 1,052 (no change)
• Package size: 317 MB (no change)
• Number of ts-expect-error directives: 365 ⬇️ 0.27% decrease vs. c76dbdd