POC +str Add StreamCollector api for unsafe transformation.

[He-Pin]

Motivation: Make it simpler when integrating with other effect system.

When reading : https://alexn.org/blog/2023/04/17/integrating-akka-with-cats-effect-3/ ; I think there should be a simpler api to integrate other effect system ,which does not need to transform back to Future.

The unsafeTransform can be implemented in similar way.

refs: https://github.com/typelevel/cats-effect/issues/3807

Related work: https://github.com/akka/akka/pull/28674 from @jrudolph

And the unsafeTransform can be implemented in similar way

Notes:

1. This is a quick POC and the api need more polish, as the unsafe statements, it's unsafe.
2. This is not a F[_] typeclass implementation.

@alexandru ping

[mdedetrich]

Also pinging @jrudolph because he did prior work on this

[He-Pin]

Now JDK22 ships a Gather https://openjdk.org/jeps/461