unbounded-spsc: Sender::send pointer-as-value transmute causes OOB read and fake-Arc drop under TX/RX race

Summary Sender::send in src/lib.rs contains an unsafe block in the DISCONNECTED arm that transmutes a raw pointer mut Producer into the bytes of a value-level Consumer. The author's intent, visible in the surrounding comment at lines 386-390, was a value transmute. The shipped code is one level o...