test: close file handles in failure mocks

[danyel117]

Summary

• close the real temporary-file handle even when a test override simulates a close failure
• preserve the simulated error and existing operation-order assertions
• unblock the Publish workflow under Bun 1.4.0, which now treats GC-closed FileHandles as errors

Verification

• Bun 1.4.0 full suite: 213 passing, 0 failures, 0 errors
• Bun 1.3.8 atomic-write suite: 29 passing
• bun run lint
• bun run typecheck
• bun run build
• bun run pack:dry-run
• Claude Opus review: APPROVE