[#355] innerring: Refactor block timer constructors

This small refactoring adds `blocktimer.go` file with
all timer related function and constructors. This way
we can create all timers in one place (at the end of
innerring.Server constructor).

To do that we had to move timer reset into global
server state so it can be accessed by netmap
processor.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/innerring/blocktimer.go

@@ -0,0 +1,61 @@
+package innerring
+
+import (
+	"github.com/nspcc-dev/neofs-node/pkg/innerring/processors/alphabet"
+	"github.com/nspcc-dev/neofs-node/pkg/innerring/processors/netmap"
+	"github.com/nspcc-dev/neofs-node/pkg/innerring/timers"
+)
+
+type (
+	epochTimerArgs struct {
+		nm *netmap.Processor // to handle new epoch tick
+
+		epochDuration uint32 // in blocks
+	}
+
+	emitTimerArgs struct {
+		ap *alphabet.Processor // to handle new emission tick
+
+		emitDuration uint32 // in blocks
+	}
+)
+
+func (s *Server) addBlockTimer(t *timers.BlockTimer) {
+	s.blockTimers = append(s.blockTimers, t)
+}
+
+func (s *Server) startBlockTimers() error {
+	for i := range s.blockTimers {
+		if err := s.blockTimers[i].Reset(); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (s *Server) tickTimers() {
+	for i := range s.blockTimers {
+		s.blockTimers[i].Tick()
+	}
+}
+
+func newEpochTimer(args *epochTimerArgs) *timers.BlockTimer {
+	epochTimer := timers.NewBlockTimer(
+		timers.StaticBlockMeter(args.epochDuration),
+		func() {
+			args.nm.HandleNewEpochTick(timers.NewEpochTick{})
+		},
+	)
+
+	return epochTimer
+}
+
+func newEmissionTimer(args *emitTimerArgs) *timers.BlockTimer {
+	return timers.NewBlockTimer(
+		timers.StaticBlockMeter(args.emitDuration),
+		func() {
+			args.ap.HandleGasEmission(timers.NewAlphabetEmitTick{})
+		},
+	)
+}