test(prodstyle): make the readiness test async so its required Timeout is enforceable

[IanFrelinger]

Why

The kernel-coverage gate has been red on master for every commit since the .NET 10 merge, for two different reasons in the same class:

commit	failure
d3d90fab	TimeoutConventionTests FAIL — the readiness test lacked Timeout
3a4ae93e (post-#348)	the readiness test itself FAIL — Tests marked with Timeout are only supported for async tests

#348 added [Fact(Timeout = TestTimeouts.HostTouching)] to satisfy the convention, but Ready_is_503_while_starting_200_once_started_and_503_again_once_stopping is synchronous, and xunit enforces Timeout by racing the returned Task against a delay — it cannot do that for a void test and fails it outright. One red was traded for another.

What

• The readiness test returns Task. Its body is still synchronous (it pins the lifetime transitions on NexoEndpoints.EvaluateReadiness directly, as the comment explains); the signature is what xunit needs to honour the timeout.
• TimeoutConventionTests now requires both halves — an explicit Timeoutand a Task return — so an unenforceable timeout is named at convention time rather than turning a passing test into a failing one. Without this the two rules contradict each other, and the next void ProdStyle test repeats the outage.
• Collapses the duplicate Fact/Theory branches: TheoryAttribute derives from FactAttribute, so the first lookup already matched theories and a Theory without a timeout was reported twice.

Verification

Locally on net10.0, TimeoutConventionTests + HealthAndReadinessProdStyleTests: 4 passed, 0 failed.

Negative check — reverting the test to void makes the convention fail with the message that names the fix:

HealthAndReadinessProdStyleTests.Ready_is_503_...: ProdStyle test has [Fact(Timeout = N)]
but returns Void; make it async Task (xunit only honours Timeout on Task-returning tests
and fails the test at run time otherwise)

The other two reds on master (Distribution Matrix Gate, Docs Link Check) are unrelated infra — Failed to download action … 429/503 from codeload.

🤖 Generated with Claude Code

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