Exposes Kotlin's Channel<Obj> to Lyng scripts as a first-class type
with rendezvous, buffered, and unlimited capacity modes. Supports
suspending send/receive, non-suspending tryReceive, close/drain
semantics, and isClosedForSend/isClosedForReceive properties.
Also fixes a pre-existing typo in BookTest.kt that blocked JVM test
compilation, and adds Channel reference docs and a parallelism.md section.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
