=str #16051 Possibility for Balance to wait for all downstream

* co-authored by @patriknw

balance-fix
+str #15205 Add FlexiRoute junction
=str  #16109: Replace ScalaGraph with custom graph impl
Merge pull request #16193 from drewhk/wip-16109-new-graph-lib-drewhk

=str  #16109: Replace ScalaGraph with custom graph impl
Merge pull request #16172 from akka/wip-15205-route-patriknw

+str #15205 Add Route junction
=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 Fix scaladoc warnings
+str #15205 Java API for FlexiRoute
+str #15802 Make TickSource cancellable

* also found a type bug in javadsl Source.subscriber
=str #15795 Add overflow protection in ActorPublisher
+str #15086 substream publishers now have subscription-timeouts