Summary

Implements the shutdownCause method for ZIO Queue as requested in issue #9844.

Changes

• Add shutdownCause(cause: Cause[Nothing]): UIO[Chunk[A]] method to Queue, Enqueue, and Dequeue traits
• Keep existing shutdown behavior unchanged (now delegates to shutdownCause)
• Implement atomic “first caller wins” semantics for concurrent shutdownCause calls
• On shutdownCause: fail pending takers and backpressured putters with the same cause
• Future queue operations (offer, take, poll, size, takeAll, takeUpTo) fail with stored cause
• awaitShutdown completes immediately when shutdownCause is called
• Return buffered items to winning caller; later callers get Chunk.empty

Testing

All existing queue tests should continue to pass. The implementation is backward compatible with the existing shutdown behavior.

/claim #9844