cp: don't panic on verbose/debug write errors

[MsfPablo]

Fixes #10554.

#13310 made the main 'src -> dest' verbose line non-panicking by buffering the write and surfacing the failure as a normal CpError::IoErrContext instead of panicking inside println!. Four remaining --verbose/--debug lines still used raw println!, so they still crashed when the stdout write failed — e.g. cp -vf /dev/null /tmp/a > /dev/full panics on the removed '<dest>' line, and cp --debug -n ... > /dev/full panics on the skipped '<dest>' line.

This converts the four remaining sites to a shared print_stdout_line helper that mirrors print_paths (BufWriter + writeln! + flush, error returned via ?):

• cp-verbose-removed in delete_path (the -v "removed" line — the cp -vf /dev/null /tmp/a > /dev/full panics #10554 repro)
• cp-debug-skipped in OverwriteMode::NoClobber::verify
• the two skipped <dest> debug lines in handle_existing_dest / handle_copy_mode (UpdateMode::None)

Output and exit codes are unchanged on the happy path; only the failure mode changes (clean error + non-zero exit instead of a panic/abort), matching GNU cp which reports write error: ... and exits non-zero.

Two Linux-gated regression tests added next to test_cp_verbose_write_error_is_reported, covering the --remove-destination -v and --debug -n paths against /dev/full.

[HackingRepo]

@MsfPablo already fixed