Function run_cp 

pub fn run_cp(
    sources: &[String],
    raw_dest: Option<&str>,
    config: &CpConfig,
) -> (Vec<String>, bool)

Determine the effective destination and perform the copy.

sources is the list of source paths; raw_dest is the positional destination (may be None when --target-directory is used).

Returns a list of per-file error messages (empty on full success) and a bool indicating whether any error occurred.