Andrej Kolchin c9aa6ba0f3
Add special error for calling metadata on $env and $nu (#11228)
Trying to call `metadata $env` or `metadata $nu` will throw an error:

```Nushell
~> metadata $nu                                                                                                                            
Error:   × Built-in variables `$env` and `$nu` have no metadata
   ╭─[entry #1:1:1]
 1 │ metadata $nu
   ·          ─┬─
   ·           ╰── no metadata available
   ╰────
```
2023-12-04 12:49:36 -06:00
..
2021-09-02 13:29:43 +12:00

nu-protocol

The nu-protocol crate holds the definitions of structs/traits that are used throughout Nushell. This gives us one way to expose them to many other crates, as well as make these definitions available to each other, without causing mutually recursive dependencies.