fix: Fix create/update metric fragment

The functions `createEventFragment` and `updateEventFragment` of the
MetaMetricsController were broken recently in the migration to
BaseControllerV2 (#28113). We ended up trying to mutate a piece of
Immer state, resulting in an error.

The affected lines were updated to use `cloneDeep` prior to mutating,
so that we're no longer attempting to mutate a frozen object.

Fixes ##28599

app/scripts/controllers/metametrics-controller.ts

@@ -1,4 +1,5 @@
 import {
+  cloneDeep,
   isEqual,
   memoize,
   merge,
@@ -584,7 +585,8 @@ export default class MetaMetricsController extends BaseController<
       : {};
 
     this.update((state) => {
-      state.fragments[id] = merge(additionalFragmentProps, fragment);
+      // @ts-expect-error this is caused by a bug in Immer, not being able to handle recursive types like Json
+      state.fragments[id] = merge(cloneDeep(additionalFragmentProps), fragment);
     });
 
     if (fragment.initialEvent) {
@@ -669,7 +671,7 @@ export default class MetaMetricsController extends BaseController<
     }
 
     this.update((state) => {
-      state.fragments[id] = merge(state.fragments[id], {
+      state.fragments[id] = merge(cloneDeep(state.fragments[id]), {
         ...payload,
         lastUpdated: Date.now(),
       });