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/lang/kclSamples.test.ts

@@ -55,18 +55,13 @@ describe('Test KCL Samples from public Github repository', () => {
     })
     // Run through all of the files in the manifest json. This will allow us to be automatically updated
     // with the latest changes in github. We won't be hard coding the filenames
-    it(
-      'should run through all the files',
-      async () => {
-        for (let i = 0; i < files.length; i++) {
-          const file: KclSampleFile = files[i]
-          const code = await getKclSampleCodeFromGithub(file.filename)
-          const parsed = parse(code)
-          assert(!(parsed instanceof Error))
-        }
-      },
-      files.length * 1000
-    )
+    files.forEach((file: KclSampleFile) => {
+      it(`should parse ${file.filename} without errors`, async () => {
+        const code = await getKclSampleCodeFromGithub(file.filename)
+        const parsed = parse(code)
+        assert(!(parsed instanceof Error))
+      }, 1000)
+    })
   })
 
   describe('when performing enginelessExecutor', () => {