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-test-support/src/playground/nu_process.rs

@@ -82,7 +82,7 @@ impl NuProcess {
 
         command.env_clear();
 
-        let paths = vec![test_bins_path()];
+        let paths = [test_bins_path()];
 
         let paths_joined = match std::env::join_paths(paths) {
             Ok(all) => all,