Tighten Cloudflare install test mock types

[alfonso-noriega]

WHY are these changes introduced?

No issue.

The Cloudflare installer tests mocked http.fetch with a partial response object cast to any. The production helper expects the node-fetch response shape, so the test can use a real Response instead of bypassing types.

WHAT is this pull request doing?

• Replaces the hand-written partial fetch response with new Response(...) from node-fetch.
• Removes the Readable stream import and the as any cast from the fetch mock.
• Preserves the same mocked status/status text and response body content.

How to test your changes?

• pnpm --filter @shopify/plugin-cloudflare vitest src/install-cloudflared.test.ts ✅
• pnpm --filter @shopify/plugin-cloudflare type-check ✅
• pnpm --filter @shopify/plugin-cloudflare lint ✅
• git diff --check ✅

Post-release steps

None.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is not user-facing; no changeset is needed.