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/std/loft.rs

@@ -68,7 +68,7 @@ async fn inner_loft(
 ) -> Result<Box<Solid>, KclError> {
     // Make sure we have at least two sketches.
     if sketches.len() < 2 {
-        return Err(KclError::Semantic(KclErrorDetails::new(
+        return Err(KclError::new_semantic(KclErrorDetails::new(
             format!(
                 "Loft requires at least two sketches, but only {} were provided.",
                 sketches.len()