Reorganize flight planning.

Previously we were trying to make every potential flight plan look
just like a strike mission's flight plan. This led to a lot of special
case behavior in several places that was causing us to misplan TOTs.

I've reorganized this such that there's now an explicit `FlightPlan`
class, and any specialized behavior is handled by the subclasses.

I've also taken the opportunity to alter the behavior of CAS and
front-line CAP missions. These no longer involve the usual formation
waypoints. Instead the CAP will aim to be on station at the time that
the CAS mission reaches its ingress point, and leave at its egress
time. Both flights fly directly to the point with a start time
configured for a rendezvous.

It might be worth adding hold points back to every flight plan just to
ensure that non-formation flights don't end up with a very low speed
enroute to the target if they perform ground ops quicker than
expected.

gen/ato.py

@@ -11,12 +11,14 @@ the single CAP flight.
 import logging
 from collections import defaultdict
 from dataclasses import dataclass, field
+from datetime import timedelta
 from typing import Dict, List, Optional
 
 from dcs.mapping import Point
 
 from theater.missiontarget import MissionTarget
 from .flights.flight import Flight, FlightType
+from .flights.flightplan import FormationFlightPlan
 
 
 @dataclass(frozen=True)
@@ -51,11 +53,67 @@ class Package:
 
     delay: int = field(default=0)
 
-    #: Desired TOT measured in seconds from mission start.
-    time_over_target: int = field(default=0)
+    #: Desired TOT as an offset from mission start.
+    time_over_target: timedelta = field(default=timedelta())
 
     waypoints: Optional[PackageWaypoints] = field(default=None)
 
+    @property
+    def formation_speed(self) -> Optional[int]:
+        """The speed of the package when in formation.
+
+        If none of the flights in the package will join a formation, this
+        returns None. This is nto uncommon, since only strike-like (strike,
+        DEAD, anti-ship, BAI, etc.) flights and their escorts fly in formation.
+        Others (CAP and CAS, currently) will coordinate in target timing but
+        fly their own path to the target.
+        """
+        speeds = []
+        for flight in self.flights:
+            if isinstance(flight.flight_plan, FormationFlightPlan):
+                speeds.append(flight.flight_plan.best_flight_formation_speed)
+        if not speeds:
+            return None
+        return min(speeds)
+
+    # TODO: Should depend on the type of escort.
+    # SEAD might be able to leave before CAP.
+    @property
+    def escort_start_time(self) -> Optional[timedelta]:
+        times = []
+        for flight in self.flights:
+            waypoint = flight.flight_plan.request_escort_at()
+            if waypoint is None:
+                continue
+            tot = flight.flight_plan.tot_for_waypoint(waypoint)
+            if tot is None:
+                logging.error(
+                    f"{flight} requested escort at {waypoint} but that "
+                    "waypoint has no TOT. It may not be escorted.")
+                continue
+            times.append(tot)
+        if times:
+            return min(times)
+        return None
+
+    @property
+    def escort_end_time(self) -> Optional[timedelta]:
+        times = []
+        for flight in self.flights:
+            waypoint = flight.flight_plan.dismiss_escort_at()
+            if waypoint is None:
+                continue
+            tot = flight.flight_plan.tot_for_waypoint(waypoint)
+            if tot is None:
+                logging.error(
+                    f"{flight} dismissed escort at {waypoint} but that "
+                    "waypoint has no TOT. It may not be escorted.")
+                continue
+            times.append(tot)
+        if times:
+            return max(times)
+        return None
+
     def add_flight(self, flight: Flight) -> None:
         """Adds a flight to the package."""
         self.flights.append(flight)