LocalFactIngestionService soft-timeout test is timing-sensitive/flaky

[simplerjiang]

• Found by: backend/API test agent and local rerun.
• Impact: CI/backend regression can fail; optional feed soft-timeout behavior may not release quickly under load.
• Repro:
  1. Run dotnet test .\backend\SimplerJiangAiAgent.Api.Tests\SimplerJiangAiAgent.Api.Tests.csproj --no-restore --logger trx;LogFileName=api-tests-20260521.trx --verbosity quiet.
  2. Observe the full suite result.
• Expected: EnsureMarketFreshAsync_WhenOptionalFeedsAreSlow_ShouldNotBlockCoreMarketRefresh finishes within its threshold.
• Actual: One full run failed with Expected soft-timeout path to finish quickly, actual=1722.8948ms; backend agent also saw single-run failures around 1787ms/2049ms.
• Claim: Assign backend/market-data owner.
• Repair: Make the test deterministic or adjust the soft-timeout implementation/threshold with a clear contract.
• Verification: Run the failed test repeatedly and then run full Api.Tests.