[1/3] Rework IP placement.

Test cases:

1. Target is not threatened.

   The IP should be placed on a direct heading from the origin to the
   target at the max ingress distance, or very near the origin airfield
   if the airfield is closer to the target than the IP distance.

2. Unthreatened home zone, max IP between origin and target, safe
   locations available for IP.

   The IP should be placed in LAR at the closest point to home.

3. Unthreatened home zone, origin within LAR, safe locations available
   for IP.

   The IP should be placed near the origin airfield to prevent
   backtracking more than needed.

4. Unthreatened home zone, origin entirely nearer the target than LAR,
   safe locations available for IP.

   The IP should be placed in LAR as close as possible to the origin.

5. Threatened home zone, safe locations available for IP.

   The IP should be placed in LAR as close as possible to the origin.

6. No safe IP.

   The IP should be placed in LAR at the point nearest the threat
   boundary.

game/data/doctrine.py

@@ -47,8 +47,13 @@ class Doctrine:
     #: fallback flight plan layout (when the departure airfield is near a threat zone).
     join_distance: Distance
 
-    #: The distance between the ingress point (beginning of the attack) and target.
-    ingress_distance: Distance
+    #: The maximum distance between the ingress point (beginning of the attack) and
+    #: target.
+    max_ingress_distance: Distance
+
+    #: The minimum distance between the ingress point (beginning of the attack) and
+    #: target.
+    min_ingress_distance: Distance
 
     ingress_altitude: Distance
 
@@ -87,9 +92,22 @@ class Doctrine:
 
     @has_save_compat_for(5)
     def __setstate__(self, state: dict[str, Any]) -> None:
-        if "ingress_distance" not in state:
-            state["ingress_distance"] = state["ingress_egress_distance"]
-            del state["ingress_egress_distance"]
+        if "max_ingress_distance" not in state:
+            try:
+                state["max_ingress_distance"] = state["ingress_distance"]
+                del state["ingress_distance"]
+            except KeyError:
+                state["max_ingress_distance"] = state["ingress_egress_distance"]
+                del state["ingress_egress_distance"]
+
+        max_ip: Distance = state["max_ingress_distance"]
+        if "min_ingress_distance" not in state:
+            if max_ip < nautical_miles(10):
+                min_ip = nautical_miles(5)
+            else:
+                min_ip = nautical_miles(10)
+            state["min_ingress_distance"] = min_ip
+
         self.__dict__.update(state)
 
 
@@ -103,7 +121,8 @@ MODERN_DOCTRINE = Doctrine(
     hold_distance=nautical_miles(15),
     push_distance=nautical_miles(20),
     join_distance=nautical_miles(20),
-    ingress_distance=nautical_miles(45),
+    max_ingress_distance=nautical_miles(45),
+    min_ingress_distance=nautical_miles(10),
     ingress_altitude=feet(20000),
     min_patrol_altitude=feet(15000),
     max_patrol_altitude=feet(33000),
@@ -139,7 +158,8 @@ COLDWAR_DOCTRINE = Doctrine(
     hold_distance=nautical_miles(10),
     push_distance=nautical_miles(10),
     join_distance=nautical_miles(10),
-    ingress_distance=nautical_miles(30),
+    max_ingress_distance=nautical_miles(30),
+    min_ingress_distance=nautical_miles(10),
     ingress_altitude=feet(18000),
     min_patrol_altitude=feet(10000),
     max_patrol_altitude=feet(24000),
@@ -175,7 +195,8 @@ WWII_DOCTRINE = Doctrine(
     push_distance=nautical_miles(5),
     join_distance=nautical_miles(5),
     rendezvous_altitude=feet(10000),
-    ingress_distance=nautical_miles(7),
+    max_ingress_distance=nautical_miles(7),
+    min_ingress_distance=nautical_miles(5),
     ingress_altitude=feet(8000),
     min_patrol_altitude=feet(4000),
     max_patrol_altitude=feet(15000),