[runtime] Harden chain verify warmup handling

[GsCommand]

Motivation

• The chain test was aborting the /verify?schema=1 request too early and did not handle a schema validator cold start, causing flaky AbortError failures in CI.
• Increase the verify window and add retry logic so the test tolerates validator warmup without changing runtime code.
• Make the verify step deterministic in CI by explicitly waiting and retrying on a 202 warmup response.

Description

• Increased the AbortController timeout for the chain verify helper from 5000ms to 10000ms in runtime/tests/runtime-signing.test.mjs to avoid premature aborts.
• Replaced the single /verify?schema=1 fetch with a bounded retry helper that logs the response status before parsing JSON, and on 202 logs validator warming, waits 1200ms, and retries once.
• Centralized warmup handling inside the test helper and removed the previous ad-hoc retry at the call site, while leaving all final assertions intact and not modifying any runtime implementation files.

Testing

• Ran the updated test file with node --test runtime/tests/runtime-signing.test.mjs and the suite passed locally.
• The updated test exercised the new timeout and retry path and completed without AbortError or flaky failures.

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Codex Task