Divorce JSON and KCL (#4436)

Removes JSON from the KCL object model. Closes https://github.com/KittyCAD/modeling-app/issues/1130 -- it was filed on Nov 27 last year. Hopefully I close it before its one year anniversary.

Changes:

- Removed the UserVal variant from `enum KclValue`. That variant held JSON data.
- Replaced it with several new variants like Number, String, Array (of KCL values), Object (where keys are String and values are KCL values)
- Added a dedicated Sketch variant to KclValue. We used to have a variant like this, but I removed it as an experimental approach to fix this issue. Eventually I decided to undo it and use the approach of this PR instead.
- Removed the `impl_from_arg_via_json` macro, which implemented conversion from KclValue to Rust types by matching the KclValue to its UserVal variant, grabbing the JSON, then deserializing that into the desired Rust type. 
- Instead, replaced it with manual conversion from KclValue to Rust types, using some convenience macros like `field!`

src/components/ModelingSidebar/ModelingPanes/MemoryPane.tsx

@@ -89,9 +89,9 @@ export const processMemory = (programMemory: ProgramMemory) => {
   const processedMemory: any = {}
   for (const [key, val] of programMemory?.visibleEntries()) {
     if (
-      (val.type === 'UserVal' && val.value.type === 'Sketch') ||
+      val.type === 'Sketch' ||
       // @ts-ignore
-      (val.type !== 'Function' && val.type !== 'UserVal')
+      val.type !== 'Function'
     ) {
       const sg = sketchFromKclValue(val, key)
       if (val.type === 'Solid') {
@@ -110,8 +110,6 @@ export const processMemory = (programMemory: ProgramMemory) => {
       processedMemory[key] = `__function(${(val as any)?.expression?.params
         ?.map?.(({ identifier }: any) => identifier?.name || '')
         .join(', ')})__`
-    } else {
-      processedMemory[key] = val.value
     }
   }
   return processedMemory