Enr fork (#967)

* Start fixing enr-fork-id

* Fix time-until-next-fork logic

* Remove fork crate

eth2/utils/slot_clock/src/lib.rs

@@ -35,6 +35,9 @@ pub trait SlotClock: Send + Sync + Sized {
     /// Returns the duration between slots
     fn slot_duration(&self) -> Duration;
 
+    /// Returns the duration from now until `slot`.
+    fn duration_to_slot(&self, slot: Slot) -> Option<Duration>;
+
     /// Returns the duration until the next slot.
     fn duration_to_next_slot(&self) -> Option<Duration>;
 

eth2/utils/slot_clock/src/manual_slot_clock.rs

@@ -135,6 +135,10 @@ impl SlotClock for ManualSlotClock {
         self.slot_duration
     }
 
+    fn duration_to_slot(&self, slot: Slot) -> Option<Duration> {
+        self.duration_to_slot(slot, *self.current_time.read())
+    }
+
     fn genesis_slot(&self) -> Slot {
         self.genesis_slot
     }

eth2/utils/slot_clock/src/system_time_slot_clock.rs

@@ -44,6 +44,11 @@ impl SlotClock for SystemTimeSlotClock {
         self.clock.slot_duration()
     }
 
+    fn duration_to_slot(&self, slot: Slot) -> Option<Duration> {
+        let now = SystemTime::now().duration_since(UNIX_EPOCH).ok()?;
+        self.clock.duration_to_slot(slot, now)
+    }
+
     fn genesis_slot(&self) -> Slot {
         self.clock.genesis_slot()
     }