Comprehensive async-suffixed saga method coverage (GH-3274)

[jeremydmiller]

Closes #3274

Background

Issue #3274 re-reports #2578: a saga handler method named with the conventional Async suffix (e.g. HandleAsync, StartAsync) is discovered as a handler but silently never wired as a saga Starting/Existing/NotFound call, so the saga never starts, cascaded continuations are dropped, and the saga parks forever — with no error or warning.

The root cause was an inconsistency: HandlerDiscovery registers both the bare name and the Async-suffixed name as valid handler methods, but SagaChain.findByNames matched the exact Method.Name with no Async variant.

The findByNames fix already shipped on main under #2578 (commit 250f5dad9), so main is not affected by the bug as reported against 5.26.0. What was missing was thorough regression coverage — the existing Bug_2578 test only spot-checks a few names.

What this PR does

Per the issue's "happy to open a PR with a regression test" offer, this adds an async clone of the synchronous saga compliance suite (GuidIdentifiedSagaComplianceSpecs / BasicWorkflow) that exercises every meaningful saga method convention end-to-end, using a genuinely async (Task-returning) body and the Async suffix:

StartAsync, StartsAsync, StartOrHandleAsync, StartsOrHandlesAsync, HandleAsync, HandlesAsync, ConsumeAsync, ConsumesAsync, OrchestrateAsync, OrchestratesAsync, and NotFoundAsync.

Each is verified at two levels:

• Discovery — the method lands in the correct StartingCalls / ExistingCalls / NotFoundCalls bucket.
• Runtime — the method is actually invoked, state is persisted/deleted, cascading messages are delivered, the [SagaIdentity] / envelope / message-property id resolution paths all work, and NotFoundAsync runs when the saga is absent.

The end-to-end assertions mirror the cloned synchronous tests (complete, cascading-id-in-header, start_1, start_2, straight update, envelope update, [SagaIdentity] update, indeterminate-id error).

Validation: reverting the findByNames Async match to strict equality fails 25 of the 26 new tests, confirming the coverage is meaningful. With the fix in place all 26 (plus the existing Bug_2578 8) pass.

Docs

• Expanded the saga Method Conventions table in docs/guide/durability/sagas.md to list the Async variant of each convention name explicitly.
• Referenced Saga handlers with Async suffix are silently not wired (discovered but excluded from Starting/Existing calls) #3274 alongside SagaChain.findByNames does not strip Async suffix; saga StartAsync / HandleAsync are discovered but silently skipped #2578 in the findByNames comment.

Note on 5.x

The bug as filed is against WolverineFx 5.26.0. The main (6.x) line already carries the fix; the 5.0 maintenance branch would need a backport of #2578's one-line findByNames change if a 5.x patch is desired.

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