Remove some unnecessary static Vecs (#11947)

Avoid unnecessary allocations or larger iterator structs

- Turn static `Vec`s into arrays when possible
- Use `std::iter::once`/`empty` where applicable
- Use `bool::then_some` in `detect column` `.chain`
- Drop in the bucket: de-vec-ing tests

crates/nu-engine/src/eval.rs

@@ -550,7 +550,7 @@ fn eval_element_with_input(
                                     // so nushell knows this result is not the last part of a command.
                                     (
                                         Some(RawStream::new(
-                                            Box::new(vec![].into_iter()),
+                                            Box::new(std::iter::empty()),
                                             None,
                                             *span,
                                             Some(0),