[statemachine] add AnyState, support transition trigger from any state

codex/utils/asyncstatemachine.nim

@@ -19,6 +19,7 @@ type
     errored*: TransitionProperty[bool]
     lastError*: ref CatchableError
   State* = ref object of RootObj
+  AnyState* = ref object of State
   Event* = proc(state: State): ?State {.gcsafe, upraises:[].}
   TransitionCondition* = proc(machine: Machine, state: State): bool {.gcsafe, upraises:[].}
   Transition* = object of RootObj
@@ -50,7 +51,7 @@ proc schedule*(machine: Machine, event: Event) =
 proc checkTransitions(machine: Machine) =
   for transition in machine.transitions:
     if transition.trigger(machine, machine.state) and
-      (machine.state == nil or machine.state == transition.prevState):
+      (machine.state == nil or machine.state == transition.prevState or transition.prevState of AnyState):
       machine.schedule(Event.transition(machine.state, transition.nextState))
 
 proc setValue*[T](prop: TransitionProperty[T], value: T) =

tests/codex/utils/testasyncstatemachine.nim

@@ -69,7 +69,7 @@ suite "async state machines":
           MyMachine(m).requestFinished.value
       ),
       Transition.new(
-        state6,
+        AnyState.new(),
         state5,
         proc(m: Machine, s: State): bool =
           MyMachine(m).errored.value