refactor(changeTracker): replace local clone() with shared clone util from @/scripts/utils

## Summary

Follow-up to #9387. The PR replaced `clone(app.nodeOutputs)` in `changeTracker.store()` with `useNodeOutputStore().snapshotOutputs()`, which internally uses the shared `clone()` utility from `@/scripts/utils` (preferring `structuredClone` with a JSON fallback over the local `JSON.parse(JSON.stringify(...))` implementation).

The remaining usages of the local `clone` function in `src/scripts/changeTracker.ts` should be migrated to use the shared utility as well.

## Remaining call sites

- `reset()`: `this.activeState = clone(state)`
- `reset()`: `this.initialState = clone(this.activeState)`
- `checkState()`: `const currentState = clone(app.rootGraph.serialize()) as ComfyWorkflowJSON`

## Proposed change

1. Remove the local `clone` function definition (~line 22 in `src/scripts/changeTracker.ts`).
2. Add `import { clone } from '@/scripts/utils'`.
3. Replace all remaining local `clone()` call sites with the imported utility.

## Context

- PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/9387
- Review comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/9387#discussion_r2887461142
- Requested by: @DrJKL

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