wc.rs: Refactor to remove `#[allow(clippy::cognitive_complexity)]`

https://github.com/uutils/coreutils/blob/main/src/uu/wc/src/wc.rs#L568

A potential way to do it:
```
    while let Some(chunk) = reader.next_strict() {
        match chunk {
            Ok(text) => process_chunk(&mut total, &text),
            Err(error) => return handle_error(error, &total),
        }
    }
```