rust-shed: move stats to the shed
rust-shed: move stats to the shed

Summary: This change also introduces a dummy no-op stats implementation for non-fbcode builds.

Reviewed By: farnz

Differential Revision: D19193954

fbshipit-source-id: f513368a2387987bf129ddf935217c90b7c84f2a

ReactiveSocket/reactivesocket-cpp,ReactiveSocket/reactivesocket-cpp,rsocket/rsocket-cpp,rsocket/rsocket-cpp,rsocket/rsocket-cpp,rsocket/rsocket-cpp,ReactiveSocket/reactivesocket-cpp