Misc tidying up around KclValue, etc. (#5653)

* Make some things a little less public

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Rename KclValue::Array to MixedArray

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Add settings to KclValue::Function

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Remove a bunch of dead code, simplifying mock exec and meaning KclValue no longer needs to deserialize

Signed-off-by: Nick Cameron <nrc@ncameron.org>

---------

Signed-off-by: Nick Cameron <nrc@ncameron.org>

rust/kcl-lib/src/execution/cad_op.rs

@@ -234,7 +234,7 @@ impl From<&KclValue> for OpKclValue {
                 ty: ty.clone(),
             },
             KclValue::String { value, .. } => Self::String { value: value.clone() },
-            KclValue::Array { value, .. } => {
+            KclValue::MixedArray { value, .. } => {
                 let value = value.iter().map(Self::from).collect();
                 Self::Array { value }
             }