make first behave same way as last: always return list when with number argument (#6616)

* make `first` behave same way as `last`

* better behaviour

* fix tests

* add tests

crates/nu-command/tests/commands/where_.rs

@@ -6,7 +6,7 @@ use nu_test_support::pipeline;
 fn filters_by_unit_size_comparison() {
     let actual = nu!(
         cwd: "tests/fixtures/formats",
-        "ls | where size > 1kib | sort-by size | get name | first 1 | str trim"
+        "ls | where size > 1kib | sort-by size | get name | first | str trim"
     );
 
     assert_eq!(actual.out, "cargo_sample.toml");
@@ -103,7 +103,7 @@ fn binary_operator_comparisons() {
             open sample.db
             | get ints
             | where z != 1
-            | first 1
+            | first
             | get z
         "#
     ));