Remove source of error in package waypoint timing.

We were calculating the TOT based on travel time to the *flight's*
target, but the ingress point based on the travel time to the target
area. If the difference in travel time between the center of the
target area and the first target were different then we'd calculate
the start time incorrectly even for single flight packages.

Seems to fix https://github.com/Khopa/dcs_liberation/issues/295

gen/flights/flightplan.py

@@ -384,40 +384,77 @@ class StrikeFlightPlan(FormationFlightPlan):
             self.split,
         } | set(self.targets)
 
+    def speed_between_waypoints(self, a: FlightWaypoint,
+                                b: FlightWaypoint) -> int:
+        # FlightWaypoint is only comparable by identity, so adding
+        # target_area_waypoint to package_speed_waypoints is useless.
+        if b.waypoint_type == FlightWaypointType.TARGET_GROUP_LOC:
+            # Should be impossible, as any package with at least one
+            # FormationFlightPlan flight needs a formation speed.
+            assert self.package.formation_speed is not None
+            return self.package.formation_speed
+        return super().speed_between_waypoints(a, b)
+
     @property
-    def tot_waypoint(self) -> Optional[FlightWaypoint]:
+    def tot_waypoint(self) -> FlightWaypoint:
         return self.targets[0]
 
+    @property
+    def target_area_waypoint(self) -> FlightWaypoint:
+        return FlightWaypoint(FlightWaypointType.TARGET_GROUP_LOC,
+                              self.package.target.position.x,
+                              self.package.target.position.y, 0)
+
+    @property
+    def travel_time_to_target(self) -> timedelta:
+        """The estimated time between the first waypoint and the target."""
+        destination = self.tot_waypoint
+        total = timedelta()
+        for previous_waypoint, waypoint in self.edges:
+            if waypoint == self.tot_waypoint:
+                # For anything strike-like the TOT waypoint is the *flight's*
+                # mission target, but to synchronize with the rest of the
+                # package we need to use the travel time to the same position as
+                # the others.
+                total += self.travel_time_between_waypoints(
+                    previous_waypoint, self.target_area_waypoint)
+                break
+            total += self.travel_time_between_waypoints(previous_waypoint,
+                                                        waypoint)
+        else:
+            raise PlanningError(
+                f"Did not find destination waypoint {destination} in "
+                f"waypoints for {self.flight}")
+        return total
+
     @property
     def mission_speed(self) -> int:
         return GroundSpeed.for_flight(self.flight, self.ingress.alt)
 
     @property
     def join_time(self) -> timedelta:
-        ingress_time = self.tot_for_waypoint(self.ingress)
         travel_time = self.travel_time_between_waypoints(
             self.join, self.ingress)
-        return ingress_time - travel_time
+        return self.ingress_time - travel_time
 
     @property
     def split_time(self) -> timedelta:
-        egress_time = self.tot_for_waypoint(self.egress)
         travel_time = self.travel_time_between_waypoints(
             self.egress, self.split)
-        return egress_time + travel_time
+        return self.egress_time + travel_time
 
     @property
     def ingress_time(self) -> timedelta:
         tot = self.package.time_over_target
         travel_time = self.travel_time_between_waypoints(
-            self.ingress, self.tot_waypoint)
+            self.ingress, self.target_area_waypoint)
         return tot - travel_time
 
     @property
     def egress_time(self) -> timedelta:
         tot = self.package.time_over_target
         travel_time = self.travel_time_between_waypoints(
-            self.tot_waypoint, self.egress)
+            self.target_area_waypoint, self.egress)
         return tot + travel_time
 
     def tot_for_waypoint(self, waypoint: FlightWaypoint) -> Optional[timedelta]: