Fix typos and use more idiomatic assertions (#7755)

I have changed `assert!(a == b)` calls to `assert_eq!(a, b)`, which give
better error messages. Similarly for `assert!(a != b)` and
`assert_ne!(a, b)`. Basically all instances were comparing primitives
(string slices or integers), so there is no loss of generality from
special-case macros,

I have also fixed a number of typos in comments, variable names, and a
few user-facing messages.

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

@@ -34,7 +34,7 @@ mod simple {
     }
 
     #[test]
-    fn double_open_curly_evalutes_to_a_single_curly() {
+    fn double_open_curly_evaluates_to_a_single_curly() {
         Playground::setup("parse_test_regex_2", |dirs, _sandbox| {
             let actual = nu!(
                 cwd: dirs.test(), pipeline(