Review async integration in cats-effect backends

[adamw]

Reading @djspiewak's release notes for cats-effect 3.5.0 RC1 got me checking if we integrate properly. And I think not:

• in the HttpClientBackend, we cancel the CompletableFuture, however shouldn't we also wait for the future to finish, to be in-line with how cats-effect integrations should work? (also in ws handlers)
• the Armeria integration uses a noop canceller, I guess we can't do much, except here and here, but how to wait for the response's completion?
• async http client seems to have a similar issue as http client one: we don't wait for the future to complete (also in stream handlers and ws handlers)
• ok http: same as above, we cancel but don't wait