Added TimeoutManager item retention

[mkatychev]

TimeoutManager can now hold a Copy item (to be returned to sender) for a set amount of time:

rex-sm/src/timeout.rs

Lines 172 to 176 in efb8b50

	pub enum Operation<T> {
	Cancel,
	Set(Instant),
	Retain(T, Instant),
	}

This opens the way for retry logic implementations that can re-run on a cadence without blocking StateMachine processors.

• StateMachine::process is not a sync method
• StateId is now part of the SmContext:
  

  rex-sm/src/manager.rs

  Lines 129 to 134 in 0bbc754

  	pub struct SmContext<K: Rex> {
  	pub signal_queue: SignalQueue<K>,
  	pub notification_queue: NotificationQueue<K::Message>,
  	pub state_store: Arc<StateStore<StateId<K>, K::State>>,
  	pub id: StateId<K>,
  	}

• Added timeout::Timeout trait for Kinds that handle timeout items:
  

  rex-sm/src/timeout.rs

  Lines 159 to 166 in efb8b50

  	pub trait Timeout: Rex
  	where
  	Self::Message: TimeoutMessage<Self>,
  	{
  	fn return_item(&self, _item: RetainItem<Self>) -> Option<Self::Input> {
  	None
  	}
  	}

• Added timeout::TimeoutMessage for RexMessages that handle timeoue items:
  

  rex-sm/src/timeout.rs

  Lines 150 to 157 in efb8b50

  	pub trait TimeoutMessage<K: Rex>:
  	std::fmt::Debug
  	+ RexMessage
  	+ From<UnaryRequest<K, Operation<Self::Item>>>
  	+ TryInto<UnaryRequest<K, Operation<Self::Item>>, Error = Report<ConversionError>>
  	{
  	type Item: Copy + Send + std::fmt::Debug;
  	}

[jsgoyette]

Suggested change

	sm.process(ctx.init(id), input);
	continue;
	sm.process(ctx.init(id), input);

[mergify]

[✅] @mkatychev: Added TimeoutManager item retention has been merged successfully.