CCOR-13153 - blocking/async void hot path causes excessive task-update latency

[chrishagglund-ship-it]

Thread starvation and broken async patterns (async void)

This is the core latency problem. The worker's hot path — WorkOnce, ProcessTasks, ProcessTask — were all declared async void instead of async Task. In C#, async void methods are fire-and-forget: the caller has no way to await them, and any exception after the first await becomes an unobserved thread-pool exception. The consequences were:

• The poll loop re-entered immediately without waiting for the current batch of tasks to complete, because WorkOnce returned void and couldn't be awaited. The RunningWorkerDone() monitor count drifted from reality.
• Thread.Sleep was used everywhere (poll interval, error backoff, retry backoff), which blocks thread-pool threads instead of releasing them. Under load, this could starve the thread pool — the very thing that async/await exists to prevent.
• The PollTask and UpdateTask API calls in TaskResourceApi were fake-async — they wrapped synchronous HTTP calls in Task.FromResult(...), so even the nominal async path blocked a thread.

The fix converts all async void to async Task, replaces all Thread.Sleep with await Task.Delay, and introduces truly async PollTaskAsync/UpdateTaskAsync/CallApiAsync methods that use RestClient.ExecuteAsync end-to-end.

Miscellaneous bugs

• Cancellation check was inverted: In ProcessTask's finally block, the condition was == CancellationToken.None instead of !=, meaning the cancellation token was never checked when an actual token was provided.
• Shutdown hot-loop: When OperationCanceledException was caught in the worker loop, it slept 10ms and re-entered while(true), immediately re-throwing — creating an infinite tight loop on shutdown. Now it cleanly breaks out of the loop.
• RecordUncaughtException() lost the exception type: It was a bare counter increment with no labels, so you couldn't tell what kind of exception was occurring.

[chrishagglund-ship-it]

I might want to reduce this to just the first commit since the 2nd commit is more of a "fix this across the board" type of thing