priortize ally ports and close ports (#335)

2x more likely to trade with ports belonging to an ally OR close.
3x more likely to trade with ports belonging to an ally AND close.
Add trading tests

src/core/game/PlayerImpl.ts

@@ -953,4 +953,38 @@ export class PlayerImpl implements Player {
       return false;
     }
   }
+
+  // It's a probability list, so if an element appears twice it's because it's
+  // twice more likely to be picked later.
+  tradingPorts(port: Unit): Unit[] {
+    let ports = this.mg
+      .players()
+      .filter((p) => p != port.owner() && p.canTrade(port.owner()))
+      .flatMap((p) => p.units(UnitType.Port))
+      .sort((p1, p2) => {
+        return (
+          this.mg.manhattanDist(port.tile(), p1.tile()) -
+          this.mg.manhattanDist(port.tile(), p2.tile())
+        );
+      });
+
+    // Make close ports twice more likely by putting them again
+    for (
+      let i = 0;
+      i < this.mg.config().proximityBonusPortsNb(ports.length);
+      i++
+    ) {
+      ports.push(ports[i]);
+    }
+
+    // Make ally ports twice more likely by putting them again
+    this.mg
+      .players()
+      .filter((p) => p != port.owner() && p.canTrade(port.owner()))
+      .filter((p) => p.isAlliedWith(port.owner()))
+      .flatMap((p) => p.units(UnitType.Port))
+      .forEach((p) => ports.push(p));
+
+    return ports;
+  }
 }