test: deflake use-cache-size-zero warm reload (#97421)
## Summary
Keep the first warm reload assertion focused on browser-visible
stale-while-revalidate behavior, then poll the route with independent
HTTP requests until a later response observes the fresh value. After
convergence, perform one final browser reload to confirm the
user-visible path also receives an updated value.
This avoids fixed delays, cache debug logging, and repeated browser
navigations that can cancel or outpace background regeneration. The
convergence poll uses the standard 3-second `retry()` window and returns
as soon as freshness is observed; the browser only reloads again after
that condition is satisfied.
## Verification
- `__NEXT_EXPERIMENTAL_STRICT_ROUTE_TYPES=true NEXT_TEST_CI=true
HEADLESS=true pnpm test-dev-webpack
test/development/app-dir/use-cache-size-zero/use-cache-size-zero.test.ts`
- `__NEXT_EXPERIMENTAL_STRICT_ROUTE_TYPES=true NEXT_TEST_CI=true
HEADLESS=true pnpm test-dev-turbo
test/development/app-dir/use-cache-size-zero/use-cache-size-zero.test.ts`
<!-- NEXT_JS_LLM -->
