KCL: Use named fields for KclError (#7321)

We've changed the unnamed field of `KclError` variants to a named called `details`.

To clarify: previously KCL errors looked like this:

```rust
pub enum KclError {
    Lexical(KclErrorDetails),
    Syntax(KclErrorDetails),
```

Now they look like this:

```rust
pub enum KclError {
    Lexical { details: KclErrorDetails },
    Syntax { details: KclErrorDetails },
}
```

This lets us more easily add fields to the errors. For example, in the UndefinedValue case, adding a field for what the undefined name was. This PR refactors the code to make my PR in https://github.com/KittyCAD/modeling-app/pull/7309 much easier.

Pure refactor, should not change any behaviour.

rust/kcl-lib/src/parsing/parser.rs

@@ -4412,7 +4412,7 @@ secondExtrude = startSketchOn(XY)
     #[test]
     fn test_parse_parens_unicode() {
         let result = crate::parsing::top_level_parse("(ޜ");
-        let KclError::Lexical(details) = result.0.unwrap_err() else {
+        let KclError::Lexical { details } = result.0.unwrap_err() else {
             panic!();
         };
         // TODO: Better errors when program cannot tokenize.