use scala 3 libs in scala 3 build

[pjfanning]

Pekko supports Scala 3.

It is not recommended for libs to depend on the cross for behaviour.
https://www.scala-lang.org/blog/2021/04/08/scala-3-in-sbt.html -- see the disclaimer

DISCLAIMER FOR LIBRARY MAINTAINERS
Using the interoperability between Scala 2.13 and Scala 3 in a published library is generally not safe for your end-users. Unless you know exactly what you are doing, it is discouraged to publish a Scala 3 library that depends on a Scala 2.13 library (the scala-library being excluded) or vice versa. The reason is to prevent library users from ending up with two conflicting versions foo_2.13 and foo_3 of the same foo library in their classpath, this problem being unsolvable in some cases.

[wlk]

Thank you, I'll release new version soon

[wlk]

1.0.1 has been released