Improve with-env robustness (#12523)

# Description
Work for #7149

- **Error `with-env` given uneven count in list form**
- **Fix `with-env` `CantConvert` to record**
- **Error `with-env` when given protected env vars**
- **Deprecate list/table input of vars to `with-env`**
- **Remove examples for deprecated input**

# User-Facing Changes

## Deprecation of the following forms

```
> with-env [MYENV "my env value"] { $env.MYENV }
my env value

> with-env [X Y W Z] { $env.X }
Y

> with-env [[X W]; [Y Z]] { $env.W }
Z
```

## recommended standardized form

```
# Set by key-value record
> with-env {X: "Y", W: "Z"} { [$env.X $env.W] }
╭───┬───╮
│ 0 │ Y │
│ 1 │ Z │
╰───┴───╯
```

## (Side effect) Repeated definitions in an env shorthand are now
disallowed

```
> FOO=bar FOO=baz $env
Error: nu:🐚:column_defined_twice

  × Record field or table column used twice: FOO
   ╭─[entry #1:1:1]
 1 │ FOO=bar FOO=baz $env
   · ─┬─     ─┬─
   ·  │       ╰── field redefined here
   ·  ╰── field first defined here
   ╰────
```

tests/shell/pipeline/commands/external.rs

@@ -133,26 +133,27 @@ fn command_not_found_error_shows_not_found_1() {
 #[test]
 fn command_substitution_wont_output_extra_newline() {
     let actual = nu!(r#"
-        with-env [FOO "bar"] { echo $"prefix (nu --testbin echo_env FOO) suffix" }
+        with-env { FOO: "bar" } { echo $"prefix (nu --testbin echo_env FOO) suffix" }
         "#);
     assert_eq!(actual.out, "prefix bar suffix");
 
     let actual = nu!(r#"
-        with-env [FOO "bar"] { (nu --testbin echo_env FOO) }
+        with-env { FOO: "bar" } { (nu --testbin echo_env FOO) }
         "#);
     assert_eq!(actual.out, "bar");
 }
 
 #[test]
 fn basic_err_pipe_works() {
-    let actual = nu!(r#"with-env [FOO "bar"] { nu --testbin echo_env_stderr FOO e>| str length }"#);
+    let actual =
+        nu!(r#"with-env { FOO: "bar" } { nu --testbin echo_env_stderr FOO e>| str length }"#);
     assert_eq!(actual.out, "3");
 }
 
 #[test]
 fn basic_outerr_pipe_works() {
     let actual = nu!(
-        r#"with-env [FOO "bar"] { nu --testbin echo_env_mixed out-err FOO FOO o+e>| str length }"#
+        r#"with-env { FOO: "bar" } { nu --testbin echo_env_mixed out-err FOO FOO o+e>| str length }"#
     );
     assert_eq!(actual.out, "7");
 }
@@ -160,7 +161,7 @@ fn basic_outerr_pipe_works() {
 #[test]
 fn err_pipe_with_failed_external_works() {
     let actual =
-        nu!(r#"with-env [FOO "bar"] { nu --testbin echo_env_stderr_fail FOO e>| str length }"#);
+        nu!(r#"with-env { FOO: "bar" } { nu --testbin echo_env_stderr_fail FOO e>| str length }"#);
     assert_eq!(actual.out, "3");
 }