Timeouts in structured concurrency

[Holo The Sage Wolf]

Hello Loom devs,
Few years ago I experimented in a personal PoC project with
StructuredConcurrency in Java 19 and I had to stop working on it for
personal reasons.

Recently I came back to the project and updated it to Java 25 and had to
change my code to the new way the API is built and while doing that I
noticed a couple of stuff I want to point out:

1. The default Joiner method can't receive timeout
Obviously that is wrong, but the API and JavaDoc don't actually help you.
Say you start with:
 ```java
try (var scope =  StructuredTaskScope.open()) {
    ...
}
```
And I want to evolve the code to add timeout, I look at
the StructuredTaskScope static methods, and won't see any way to do that.
After reading a bit what StructuredTaskScope.open(Joiner, configFunction)
does, I will realise that I can set the timeout using the configFunction.
But then I will encounter the problem that I need to provide a Joiner,
currently the only way to actually get the "no args method"-joiner is to
look at the source code of the method, see which Joiner it uses and copy
that into my method to get:
 ```java
try (var scope =
StructuredTaskScope.open(Joiner.awaitAllSuccessfulOrThrow(), (conf) ->
...)) {
    ...
}
```
Not only is this a lot of work to do something very simple, there is a high
chance that people who start learning concurrency will want to use timeout
before they even know what the Joiner object is.

2. Changing only the timeout is "verbose".
I can only talk from my experience, so I may have the wrong impression, but
I feel like setting timeout is orders of magnitude more common than
changing the default ThreadFactory (especially when using virtual threads)
or setting a name.
I feel like adding a couple of overloads of the open method that takes only
an extra parameter of duration will be convenient:
> StructuredTaskScope.open()
> StructuredTaskScope.open(Duration timeout)
> StructuredTaskScope.open(Joiner joiner)
> StructuredTaskScope.open(Joiner joiner, Duration timeout)
> StructuredTaskScope.open(Joiner joiner, Function<Configuration,
Configuration> configFunction)
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