Make mailbox push infallible and replace the locked tick-timing buffer with a
lock-free ring.
- channel: HybridChannel::push and Sender::send now return () — overflow always
absorbs, never rejects — dropping the Result<(), T> surface and its callers.
- stats: tick_timings moves from Mutex<VecDeque> to a lock-free crossbeam
ArrayQueue (drop-oldest-on-full), removing the per-tick lock.
- ripple the signature change through worker/runtime/config; drop worker_benchmarks.
- expand runtime_api tests around the new channel/stats shapes.
Signed-off-by: Zachery Aaron Shores-Chmielewski <zacheryasc@gmail.com>
