[fix] Remove dynamic import timing issue causing Playwright test flakiness

[christian-byrne]

Fixes the deferred timing condition introduced in PR #3955 that was causing multiple Playwright tests to become flaky.

Problem:
PR #3955 refactored file handling by introducing a dynamic import in the handleFile method:

const { getFileHandler } = await import('@/utils/fileHandlers')

Fixes #4029.

┆Issue is synchronized with this Notion page by Unito

[christian-byrne]

Test report:

Running 337 tests using 2 workers
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  1) [chromium] › tests/widget.spec.ts:181:3 › Image widget › Can change image by changing the filename combo value 

    Test timeout of [15](https://github.com/Comfy-Org/ComfyUI_frontend/actions/runs/15357823358/job/43220311580?pr=4031#step:7:16)000ms exceeded.

    Error: locator.click: Test timeout of 15000ms exceeded.
    Call log:
      - waiting for getByRole('menuitem', { name: 'image32x32.webp' })


      194 |       name: 'image32x32.webp'
      195 |     })
    > 196 |     await comboEntry.click({ noWaitAfter: true })
          |                      ^
      197 |
      198 |     // Expect the image preview to change automatically
      199 |     await expect(comfyPage.canvas).toHaveScreenshot(

        at /home/runner/work/ComfyUI_frontend/ComfyUI_frontend/ComfyUI_frontend/browser_tests/tests/widget.spec.ts:196:22

  1 flaky
    [chromium] › tests/widget.spec.ts:[18](https://github.com/Comfy-Org/ComfyUI_frontend/actions/runs/15357823358/job/43220311580?pr=4031#step:7:19)1:3 › Image widget › Can change image by changing the filename combo value 
  28 skipped
  308 passed (11.8m)