reduce number of trade ships by 50%, double gold per trade ship (#1934)

## Description:

v25 increased the number of trade ships from v24, causing lag
complaints. On my chromebook pathfinding is using over 60% of cpu.

So reduced the number of trade ships roughly by half, but double the
gold per trade ship so it should balance out,

World v25: 
* 2 mins: ~ 60 trade ships 
* 5 mins: ~ 140 trade ships

World on this branch:
* 2 mins: ~ 35 trade ships
* 5 mins: ~ 70 trade ships


Also increased the probably of trade ship spawn for players with under 2
tradeships to prevent larger players from starving out smaller players.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

src/core/configuration/Config.ts

@@ -130,7 +130,11 @@ export interface Config {
   defaultDonationAmount(sender: Player): number;
   unitInfo(type: UnitType): UnitInfo;
   tradeShipGold(dist: number, numPorts: number): Gold;
-  tradeShipSpawnRate(numTradeShips: number, numPlayerPorts: number): number;
+  tradeShipSpawnRate(
+    numTradeShips: number,
+    numPlayerPorts: number,
+    numPlayerTradeShips: number,
+  ): number;
   trainGold(rel: "self" | "friendly" | "other"): Gold;
   trainSpawnRate(numPlayerFactories: number): number;
   trainStationMinRange(): number;

src/core/configuration/DefaultConfig.ts

@@ -355,7 +355,7 @@ export class DefaultConfig implements Config {
   }
 
   tradeShipGold(dist: number, numPorts: number): Gold {
-    const baseGold = Math.floor(50_000 + 50 * dist);
+    const baseGold = Math.floor(100_000 + 100 * dist);
     const numPortBonus = numPorts - 1;
     // Hyperbolic decay, midpoint at 5 ports, 3x bonus max.
     const bonus = 1 + 2 * (numPortBonus / (numPortBonus + 5));
@@ -363,19 +363,31 @@ export class DefaultConfig implements Config {
   }
 
   // Probability of trade ship spawn = 1 / tradeShipSpawnRate
-  tradeShipSpawnRate(numTradeShips: number, numPlayerPorts: number): number {
+  tradeShipSpawnRate(
+    numTradeShips: number,
+    numPlayerPorts: number,
+    numPlayerTradeShips: number,
+  ): number {
     // Geometric mean of base spawn rate and port multiplier
     const combined = Math.sqrt(
-      this.tradeShipBaseSpawn(numTradeShips) *
+      this.tradeShipBaseSpawn(numTradeShips, numPlayerTradeShips) *
         this.tradeShipPortMultiplier(numPlayerPorts),
     );
 
-    return Math.floor(12 / combined);
+    return Math.floor(25 / combined);
   }
 
-  private tradeShipBaseSpawn(numTradeShips: number): number {
-    const decayRate = Math.LN2 / 30;
-    return 1 - sigmoid(numTradeShips, decayRate, 100);
+  private tradeShipBaseSpawn(
+    numTradeShips: number,
+    numPlayerTradeShips: number,
+  ): number {
+    if (numPlayerTradeShips < 3) {
+      // If other players have many ports, then they can starve out smaller players.
+      // So this prevents smaller players from being completely starved out.
+      return 1;
+    }
+    const decayRate = Math.LN2 / 10;
+    return 1 - sigmoid(numTradeShips, decayRate, 55);
   }
 
   private tradeShipPortMultiplier(numPlayerPorts: number): number {

src/core/execution/PortExecution.ts

@@ -79,9 +79,10 @@ export class PortExecution implements Execution {
   shouldSpawnTradeShip(): boolean {
     const numTradeShips = this.mg.unitCount(UnitType.TradeShip);
     const numPlayerPorts = this.player.unitCount(UnitType.Port);
+    const numPlayerTradeShips = this.player.unitCount(UnitType.TradeShip);
     const spawnRate = this.mg
       .config()
-      .tradeShipSpawnRate(numTradeShips, numPlayerPorts);
+      .tradeShipSpawnRate(numTradeShips, numPlayerPorts, numPlayerTradeShips);
     for (let i = 0; i < this.port!.level(); i++) {
       if (this.random.chance(spawnRate)) {
         return true;