test: resolve xUnit analyzer warnings for a warning-free build

[FranRuiz98]

What & why

The library project already built clean, but the test project emitted 157 analyzer warnings, so the solution as a whole was never warning-free — against the repo convention of zero compiler warnings.

• 154 × xUnit1051 — "Calls to methods which accept CancellationToken should use TestContext.Current.CancellationToken"
• 3 × xUnit1031 — blocking Task.Result access in a test method

Changes

Passed TestContext.Current.CancellationToken to every flagged call across 19 test files:
HttpClient.GetAsync/PostAsync, Task.Delay, content ReadAsStringAsync/ReadAsByteArrayAsync/ReadFromJsonAsync, ICacheStore.GetAsync/SetAsync/RemoveAsync, and RequestCoalescer.ExecuteAsync — including calls whose argument list spans multiple lines around a lambda.

Replaced the blocking Task.Result accesses in ConditionalRequestCoalescingTests with awaited results (which also made the preceding Task.WhenAll redundant).

Notes for reviewer

• Edits were driven off the analyzer's exact reported positions, not a blanket find/replace — so calls that already pass a token (e.g. Task.Delay(delay, ct) inside test helper stubs) are untouched.
• No library code changed — test files only. The diff is 158 insertions / 157 deletions, almost entirely 1:1 line replacements.
• One blocking call is intentionally left at Caching/StaleWhileRevalidateTests.cs:57 (gate.Task.GetAwaiter().GetResult()). It sits in a synchronous stub-handler lambda rather than a test method, so xUnit1031 does not apply, and it is load-bearing: it deliberately blocks the background stale-while-revalidate call so the test can assert the stale response is served immediately. The zero warning count is genuine, not achieved by suppression.

Verification

• Clean --no-incremental rebuild of the full solution: 0 warnings, 0 errors (xUnit1031: 0, xUnit1051: 0).
• All 343 tests pass.

🤖 Generated with Claude Code