=str #16221 fix graph precondition checks when attaching Source/Sink
!str Remove unused io2 package
Merge pull request #16225 from 2m/wip-16221-graph-source-sink-preconditions

=str #16221 fix graph precondition checks when attaching Source/Sink
=str #16163 allow connecting GraphSource to GraphSink directly

* introduce Identity junction, which is used to connect GraphSource to GraphSink
* only materialize ActorFlowSource and ActorFlowSink as a Flow
Merge pull request #16222 from 2m/wip-16163-graph-source-to-graph-sink

=str #16163 allow connecting GraphSource to GraphSink directly
+str: Implement efficient stream op DSL
Merge pull request #16129 from drewhk/wip-pushpull-drewhk

+str: Implement efficient stream op DSL
Merge pull request #16229 from akka/wip-rm-io2-patriknw

!str Remove unused io2 package
+str #16105 Java API for FlexiMerge
Merge pull request #16218 from akka/wip-16105-java-FlexiMerge-patriknw

+str #16105 Java API for FlexiMerge
+str #15802 Make TickSource cancellable

* also found a type bug in javadsl Source.subscriber