Add compat flag for queue consumers to not block on waitUntil'ed work

[a-robinson]

The intent is that the event can be considered done when the
queue() handler's returned promise resolves, allowing acked/nacked
message info to be returned back to the queues infrastructure sooner,
rather than requiring all waitUntil'ed work to finish first. This has
two important benefits:

1. This will keep consumer invocations from getting slowed down by
   slow/hung waitUntil'ed tasks.
2. This will keep consumer invocations from failing due to failing
   waitUntil tasks.

This notably makes queue() handlers behave more like fetch() handlers, which should make them more intuitive for most users.

[jasnell]

@fhanau ... this will likely impact the scheduling of the Outcome event for streaming tail workers.

[a-robinson]

Fixed up the code to implement the decisions for the two questions above. There's a lot of test coverage in the corresponding internal PR, so from my perspective this is good to go.

[a-robinson]

Ughh the linter doesn't like something about the formatting -- forgive any small force pushes for a little bit while I try to fix it since I guess the version of the formatter that I'm running locally isn't up to date anymore, but I've never been able to get the tooling in this repo to work :|

[a-robinson]

Ughh the linter doesn't like something about the formatting -- forgive any small force pushes for a little bit while I try to fix it since I guess the version of the formatter that I'm running locally isn't up to date anymore, but I've never been able to get the tooling in this repo to work :|

Ok, looks like it was just the one line that the linter was unhappy with -- it's passing now.

So this just needs review from someone on the runtime team, since @jbwcloudflare doesn't count.

[jasnell]

LGTM but I'd like to see some additional code comments explaining the code flow a bit more. With the promise chains it becomes a bit obtuse very quickly

[a-robinson]

Thanks for the review!