fix(ajax): retain response status in cached results

[xu91102]

Cache the original response status together with content and options, and pass it to callbacks on cache hits. Previously, revisiting a cached page set vm.route.response to undefined, even though the first visit provided { ok, status, statusText }.

Fixes #2812.

Added a regression through the public AJAX helper, mocking only XMLHttpRequest. It compares the complete callback payload for the initial request and the cached request.

Validation:

• Regression failed before the fix because the cached response was undefined, then passed.
• npm run test:jest -- --runInBand: 14 suites, 125 tests, 46 snapshots passed.
• npm run typecheck and npm run build: passed.
• Prettier/ESLint checks for changed files and git diff --check: passed.

Assisted by Codex; reviewed the full diff and ran these checks locally. The full Playwright browser matrix was not run locally.

[vercel]

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[Koooooo-7]

LGTM.