f0a8bf2: test: remove flaky basic_expiry integration test (#695)

* test: remove flaky basic_expiry integration test

* test: fix flaky test_route_with_one_healthy_and_one_unhealthy_seed

Replace fixed sleep durations with retry loops that actively poll for expected routing state. This eliminates timing-related flakiness in CI environments where task scheduling is less predictable.

Changes:
- Add wait_for_routing_to_domains helper that polls until expected domains are available
- Update test to use retry loops with timeouts instead of fixed sleeps
- Remove timing assumptions that failed in CI due to scheduler variance

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

* test: improve wait_for_routing_to_domains reliability

Increase sample sizes and timeouts to account for CI environment variability:
- Use 10 samples for single domain, 30 for multiple (matching other tests)
- Calculate timeouts based on snapshot_update_duration (fetch + 2*check intervals)
- Increase poll interval to 100ms to reduce overhead

These changes align with the timing patterns used in other routing tests and provide sufficient margin for CI scheduler variance.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

* Revert "test: improve wait_for_routing_to_domains reliability"
Revert "test: fix flaky test_route_with_one_healthy_and_one_unhealthy_seed"

These commits attempted to fix the flaky test with retry logic, but the test continues to fail in CI. Reverting to consider alternative approaches.

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Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>