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
   ╰────
```

src/tests/test_env.rs

@@ -1,4 +1,4 @@
-use crate::tests::{run_test, TestResult};
+use crate::tests::{fail_test, run_test, TestResult};
 
 #[test]
 fn shorthand_env_1() -> TestResult {
@@ -7,7 +7,7 @@ fn shorthand_env_1() -> TestResult {
 
 #[test]
 fn shorthand_env_2() -> TestResult {
-    run_test(r#"FOO=BAZ FOO=MOO $env.FOO"#, "MOO")
+    fail_test(r#"FOO=BAZ FOO=MOO $env.FOO"#, "defined_twice")
 }
 
 #[test]