refactor(cp): replace println! with write_stdout_line for robust error #15609

Job	Run time
Style/Python	8s
Style/spelling (ubuntu-latest, feat_os_unix)	16s
Pre-commit hooks	28s
Style/format (ubuntu-latest, feat_os_unix)	15s
Style/lint (windows-latest, feat_os_windows)	55s
Style/lint (ubuntu-latest, all, true)	54s
Style/lint (macos-latest, feat_os_macos)	53s
Style/toml	12s
	4m 1s

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