fix(hmr): run HMR handler sequentially

[sapphi-red]

Description

This PR aims to fix the following flaky fail:

FAIL playground/hmr/tests/hmr.spec.ts > invalidate works with multiple tabs
AssertionError: expected '>>> vite:beforeUpdate -- update' to match '>>> vite:invalidate -- /invalidation/…'
Expected: ">>> vite:invalidate -- /invalidation/child.js"
Received: ">>> vite:beforeUpdate -- update"
https://github.com/vitejs/vite/actions/runs/13994683432/job/39186785003#step:12:214

This fail was happening because multiple HMR event was processed concurrently.
This PR makes the HMR event handler to run sequentially. This makes the HMR behavior in browsers more aligned with the module runner.

I tested this locally with the following test:

  test.only('invalidate works with multiple tabs', async () => {
    const pages: Page[] = []
    try {
      for (let i = 0; i < 10; i++) {
        const p = await browser.newPage()
        await p.goto(viteTestUrl)
        pages.push(p)
      }

      for (let i = 0; i < 30; i++) {
        browserLogs.length = 0
        console.log('update!')

        const el = await page.$('.invalidation-parent')
        await untilBrowserLogAfter(
          () =>
            editFile('invalidation/child.js', (code) =>
              code.replace('child', 'child updated'),
            ),
          [
            '>>> vite:beforeUpdate -- update',
            '>>> vite:invalidate -- /invalidation/child.js',
            '[vite] invalidate /invalidation/child.js',
            '[vite] hot updated: /invalidation/child.js',
            '>>> vite:afterUpdate -- update',
            // if invalidate dedupe doesn't work correctly, this beforeUpdate will be called twice
            '>>> vite:beforeUpdate -- update',
            '(invalidation) parent is executing',
            '[vite] hot updated: /invalidation/parent.js',
            '>>> vite:afterUpdate -- update',
          ],
          true,
        )
        await untilUpdated(() => el.textContent(), 'child updated')
        console.log('update done!')
        await new Promise((r) => setTimeout(r, 10))
        editFile('invalidation/child.js', (code) =>
          code.replace('child updated', 'child'),
        )
        await untilUpdated(() => el.textContent(), /^child$/)
        await new Promise((r) => setTimeout(r, 30))
      }
    } finally {
      await Promise.all(pages.map((p) => p.close()))
    }
  })

refs #16307

[sapphi-red]

/ecosystem-ci run

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/vite@19793

commit: eecb6e4

[vite-ecosystem-ci]

📝 Ran ecosystem CI on eecb6e4: Open

suite	result	latest scheduled
laravel	❌ failure	✅ success
storybook	❌ failure	❌ failure
vite-environment-examples	✅ success	❌ failure
vike	✅ success	❌ failure
vite-plugin-react	✅ success	❌ failure
waku	✅ success	❌ failure

✅ nuxt, quasar, histoire, ladle, previewjs, marko, analogjs, sveltekit, rakkas, vite-plugin-vue, astro, qwik, vitest, vite-plugin-pwa, vitepress, unocss, vite-plugin-react-swc, react-router, vite-setup-catalogue, vite-plugin-svelte, vuepress, vite-plugin-cloudflare

[patak-cat]

I think we can merge this one in the minor