Migrate KStream.branch() to KStream.split()

Kafka Streams 2.8 deprecated KStream.branch(Predicate...) in favor of KStream.split() (KIP-418), and Kafka 4.0 removed it. Rewrites a KStream[] declared from branch() to fill the same array through split() and Branched.withConsumer, so every use of the array keeps working, and rewrites a branch() whose result is unused to a split() chain. Records still go to the first branch whose predicate matches and are dropped when none does, and the topology consumes as many processor indexes as before, so generated state store and topic names do not change. With Named, the branch processors keep their names.