Stabilize Mocha saga integration tests against timing flakes

[glen-84]

Summary

• The four saga IntegrationTests relied on fixed Task.Delay waits before asserting on store state, which flaked under CI load: the Main Branch Coverage run had Saga_Should_TimeoutWithCustomResponse fail with Expected: 0, Actual: 1 when 500 ms wasn't enough for the timeout to propagate.
• Replaced those delays with deterministic synchronization. Each test polls the specific persisted saga state, fails fast if the expected precondition never appears, and waits for the instance to be deleted, all bounded by the existing 10 s timeout.
• The timeout tests wait until the saga is persisted before sending SagaTimedOutEvent, so it always targets a stored instance.
• Saga_Should_SupportRequestResponse uses a new GatedTriggerRequestHandler that holds the reply, parking the saga in AwaitingResponse so its persisted state is observable; releasing the reply then drives finalization and deletion.

Test plan

• dotnet test --filter-class Mocha.Sagas.Tests.IntegrationTests — 9/9 passing across multiple consecutive runs.
• Full Mocha.Sagas.Tests suite — 136 passed, 1 skipped, 0 failed.

[Copilot]

Pull request overview

Stabilizes Mocha saga integration tests by replacing fixed Task.Delay waits with deterministic synchronization against persisted saga state, reducing CI timing flakes.

Changes:

• Replaced fixed delays with bounded polling that waits for specific saga persistence/deletion conditions.
• Ensured timeout tests only send SagaTimedOutEvent after the saga instance is persisted.
• Added a gated request handler to hold replies so the AwaitingResponse persisted state can be observed deterministically.

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[github-code-quality]

Code Coverage Overview

Languages: C#

C# / code-coverage/dotnet

The overall coverage in the gai/stabilize-saga-i... branch remains at 49%, unchanged from the main branch.

Show a code coverage summary of the most impacted files.

File	main 443ea28	gai/stabilize-saga-i... b9841b3	+/-
/home/runner/wo...ageProcessor.cs	100%	89%	-11%
/home/runner/wo...toResetEvent.cs	73%	68%	-5%
/home/runner/wo...eiveEndpoint.cs	72%	69%	-3%
/home/runner/wo...DefaultTopic.cs	89%	90%	+1%
/home/runner/wo...efaultPubSub.cs	89%	91%	+2%
/home/runner/wo...ueryExecutor.cs	65%	67%	+2%
/home/runner/wo...tor/Mediator.cs	89%	91%	+2%
/home/runner/wo...PromiseCache.cs	78%	81%	+3%
/home/runner/wo...entsListener.cs	62%	66%	+4%
/home/runner/wo...heMiddleware.cs	86%	92%	+6%

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