Update .gitmodules for rbx-dom URL and enhance UnresolvedValue handling

- Changed the rbx-dom submodule URL in .gitmodules from SSH to HTTPS for easier access.
- Introduced a new method to handle OptionalCFrame variants in UnresolvedValue, allowing for better serialization by returning `None` for `OptionalCFrame(None)`.
- Updated various files to utilize the new handling logic, ensuring properties are only inserted when resolved values are available.

src/snapshot_middleware/json_model.rs

@@ -123,10 +123,11 @@ fn json_model_from_pair<'sync>(
                 }
             }
             _ => {
-                properties.insert(
-                    name,
-                    UnresolvedValue::from_variant(value.clone(), &new_inst.class, &name),
-                );
+                if let Some(resolved) =
+                    UnresolvedValue::from_variant(value.clone(), &new_inst.class, &name)
+                {
+                    properties.insert(name, resolved);
+                }
             }
         }
     }