# Description

This PR will help report a bad date that can't be converted where the
error message says `* Unable to parse datetime`. This is helpful when
you're converting a big table and it fails somewhere that you really
can't see. I put it in `[]` so that when it's null, you can see that
there should be something there.

Before:
```
> 'Tue 1 0' | into datetime 
Error: nu::shell::datetime_parse_error (link)

  × Unable to parse datetime
   ╭─[entry nushell#1:1:1]
 1 │ 'Tue 1 0' | into datetime
   · ────┬────
   ·     ╰── datetime parsing failed
   ╰────
  help: Examples of supported inputs:
         * "5 pm"
         * "2020/12/4"
         * "2020.12.04 22:10 +2"
         * "2020-04-12 22:10:57 +02:00"
         * "2020-04-12T22:10:57.213231+02:00"
         * "Tue, 1 Jul 2003 10:52:37 +0200"
```
After:
```
> 'Tue 1 0' | into datetime
Error: nu:🐚:datetime_parse_error (link)

  × Unable to parse datetime: [Tue 1 0].
   ╭─[entry nushell#4:1:1]
 1 │ 'Tue 1 0' | into datetime
   · ────┬────
   ·     ╰── datetime parsing failed
   ╰────
  help: Examples of supported inputs:
         * "5 pm"
         * "2020/12/4"
         * "2020.12.04 22:10 +2"
         * "2020-04-12 22:10:57 +02:00"
         * "2020-04-12T22:10:57.213231+02:00"
         * "Tue, 1 Jul 2003 10:52:37 +0200"
```

# User-Facing Changes

New format for the error message.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.