report which datetime couldn't be converted (#7980)

# 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:🐚:datetime_parse_error (link)

  × Unable to parse datetime
   ╭─[entry #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 #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.

crates/nu-command/src/conversions/into/datetime.rs

@@ -280,13 +280,13 @@ fn action(input: &Value, args: &Arguments, head: Span) -> Value {
                 Zone::East(i) => match FixedOffset::east_opt((*i as i32) * HOUR) {
                     Some(eastoffset) => match_datetime!(eastoffset.timestamp_opt(ts, 0)),
                     None => Value::Error {
-                        error: ShellError::DatetimeParseError(*span),
+                        error: ShellError::DatetimeParseError(input.debug_value(), *span),
                     },
                 },
                 Zone::West(i) => match FixedOffset::west_opt((*i as i32) * HOUR) {
                     Some(westoffset) => match_datetime!(westoffset.timestamp_opt(ts, 0)),
                     None => Value::Error {
-                        error: ShellError::DatetimeParseError(*span),
+                        error: ShellError::DatetimeParseError(input.debug_value(), *span),
                     },
                 },
                 Zone::Error => Value::Error {