perf: fix hang when leaving G-Code Preview page (#1949)

src/store/gcodeviewer/mutations.ts

@@ -1,15 +1,15 @@
 import { getDefaultState } from './index'
 import { MutationTree } from 'vuex'
 import { GcodeviewerState } from '@/store/gcodeviewer/types'
-import Vue from 'vue'
+import Vue, { markRaw } from 'vue'
 
 export const mutations: MutationTree<GcodeviewerState> = {
     reset(state) {
         Object.assign(state, getDefaultState())
     },
 
     setViewerBackup(state, backup) {
-        Vue.set(state, 'viewerBackup', backup)
+        Vue.set(state, 'viewerBackup', markRaw(backup) /* viewer object is large and quite slow to proxy */)
     },
 
     setCanvasBackup(state, backup) {