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
   ╰────
```

crates/nu-parser/src/parser.rs

@@ -5164,9 +5164,8 @@ pub fn parse_expression(working_set: &mut StateWorkingSet, spans: &[Span]) -> Ex
         }
     };
 
-    let with_env = working_set.find_decl(b"with-env");
-
     if !shorthand.is_empty() {
+        let with_env = working_set.find_decl(b"with-env");
         if let Some(decl_id) = with_env {
             let mut block = Block::default();
             let ty = output.ty.clone();
@@ -5176,13 +5175,12 @@ pub fn parse_expression(working_set: &mut StateWorkingSet, spans: &[Span]) -> Ex
 
             let mut env_vars = vec![];
             for sh in shorthand {
-                env_vars.push(sh.0);
-                env_vars.push(sh.1);
+                env_vars.push(RecordItem::Pair(sh.0, sh.1));
             }
 
             let arguments = vec![
                 Argument::Positional(Expression {
-                    expr: Expr::List(env_vars),
+                    expr: Expr::Record(env_vars),
                     span: span(&spans[..pos]),
                     ty: Type::Any,
                     custom_completion: None,