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This fixes an issue brought up by nihilander in
[Discord](https://discord.com/channels/601130461678272522/614593951969574961/1201594105986285649).

# Description
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Nushell panics when the spread operator is used like this (the
`...$rest` shouldn't actually be parsed as a spread operator at all):

```nu
$ def foo [...rest: string] {...$rest}                      
$ foo bar baz                                               
thread 'main' panicked at /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/nu-protocol-0.89.0/src/signature.rs:650:9:
Internal error: can't run a predeclaration without a body
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: <nu_protocol::signature::Predeclaration as nu_protocol::engine::command::Command>::run
   3: nu_engine::eval::eval_call
   4: nu_engine::eval::eval_expression_with_input
   5: nu_engine::eval::eval_element_with_input
   6: nu_engine::eval::eval_block
   7: nu_cli::util::eval_source
   8: nu_cli::repl::evaluate_repl
   9: nu::run::run_repl
  10: nu::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
```

The problem was that whenever the parser saw something like `{...$`,
`{...(`, or `{...[`, it would treat that as a record with a spread
expression, ignoring the syntax shape of the block it was parsing. This
should now be fixed, and the snippet above instead gives the following
error:

```nu
Error: nu::shell::external_command

  × External command failed
   ╭─[entry nushell#1:1:1]
 1 │  def foo [...rest] {...$rest}
   ·                     ────┬───
   ·                         ╰── executable was not found
   ╰────
  help: No such file or directory (os error 2)
```

# User-Facing Changes
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Stuff like `do { ...$rest }` will now try to run a command `...$rest`
rather than complaining that variable `$rest` doesn't exist.

# Tests + Formatting
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crates/nu-std"` to run the tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
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# After Submitting
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Sorry about the issue, I am not touching the parser again for a long
time :)