Remove redundant AtomicUsize/Ordering/Arc re-exports from common/mod.rs
and runtime_mechanics.rs. Zero warnings now.
Authored by Claude, lovingly guided by Zachery Aaron Shores-Chmielewski
Merge Watch death-notification system into swactor-std, reducing core
surface. WatchRegistry now lives alongside MonitorRegistry in StdExtension,
with CtxWatching and RuntimeWatching extension traits for the public API.
Phase 5b removed from tick_once; notifications delivered via on_actor_death
in phase 7. Core shrinks from 2,636 to 2,440 lines (-196, -7.4%).
Authored by Claude, lovingly guided by Zachery Aaron Shores-Chmielewski
Adds some basic benchmarking, stress tests. They still need to be properly examined to ensure they are testing the correct properties, but fit for "good enough". Implements the HybridChannel type, which features a channel buffer that can withstand overflows. It does so by providing a dequeue behind a mutex. Without overflow, will push messages into the lock free ArrayQueue implemented by crossbeam_queue; when that buffer fills, will use the locking portion provided by the Mutex<VecDequeue>.
In the future we can even further optimize this, perhaps with some linked list implementations of lock-free channels, but, like the benchmarks, this fits the "good enough" bar for now.
