Fix ignored clippy lints (#12160)

# Description
Fixes some ignored clippy lints.

# User-Facing Changes
Changes some signatures and return types to `&dyn Command` instead of
`&Box<dyn Command`, but I believe this is only an internal change.

crates/nu-command/src/strings/detect_columns.rs

@@ -109,7 +109,6 @@ fn detect_columns(
     let config = engine_state.get_config();
     let input = input.collect_string("", config)?;
 
-    #[allow(clippy::needless_collect)]
     let input: Vec<_> = input
         .lines()
         .skip(num_rows_to_skip.unwrap_or_default())