Factory spawns trains (#1408)

## Description:

- Change trains so it spawns from factories only
- Increase train frequency as they will now spawn from a single
structure.
- Factory will spawn more trains depending on its level
- Fix port to connect to nearby railroads
- Add factory description

## 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
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

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

IngloriousTom

---------

Co-authored-by: Tom Rouillard <trouilla@mathworks.com>
Co-authored-by: evanpelle <evanpelle@gmail.com>

src/core/execution/PortExecution.ts

@@ -2,6 +2,7 @@ import { Execution, Game, Player, Unit, UnitType } from "../game/Game";
 import { TileRef } from "../game/GameMap";
 import { PseudoRandom } from "../PseudoRandom";
 import { TradeShipExecution } from "./TradeShipExecution";
+import { TrainStationExecution } from "./TrainStationExecution";
 
 export class PortExecution implements Execution {
   private active = true;
@@ -36,6 +37,7 @@ export class PortExecution implements Execution {
         return;
       }
       this.port = this.player.buildUnit(UnitType.Port, spawn, {});
+      this.createStation();
     }
 
     if (!this.port.isActive()) {
@@ -84,4 +86,18 @@ export class PortExecution implements Execution {
     }
     return false;
   }
+
+  createStation(): void {
+    if (this.port !== null) {
+      const nearbyFactory = this.mg.hasUnitNearby(
+        this.port.tile()!,
+        this.mg.config().trainStationMaxRange(),
+        UnitType.Factory,
+        this.player.id(),
+      );
+      if (nearbyFactory) {
+        this.mg.addExecution(new TrainStationExecution(this.port));
+      }
+    }
+  }
 }