Discounts can only be used one time (#892)

## Description:

Discounts on structures and warships can only be used one time.

## 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

---------

Co-authored-by: Scott Anderson <scottanderson@users.noreply.github.com>

src/core/game/Game.ts

@@ -508,7 +508,8 @@ export interface Player {
 
   // Units
   units(...types: UnitType[]): Unit[];
-  unitsIncludingConstruction(type: UnitType): Unit[];
+  unitsConstructed(type: UnitType): number;
+  unitsOwned(type: UnitType): number;
   buildableUnits(tile: TileRef): BuildableUnit[];
   canBuild(type: UnitType, targetTile: TileRef): TileRef | false;
   buildUnit<T extends UnitType>(

src/core/game/PlayerImpl.ts

@@ -216,14 +216,41 @@ export class PlayerImpl implements Player {
     return this._units.filter((u) => ts.has(u.type()));
   }
 
-  unitsIncludingConstruction(type: UnitType): Unit[] {
-    const units = this.units(type);
-    units.push(
-      ...this.units(UnitType.Construction).filter(
-        (u) => u.constructionType() === type,
-      ),
-    );
-    return units;
+  private numUnitsConstructed: number[] = [];
+  private recordUnitConstructed(type: UnitType): void {
+    if (type in this.numUnitsConstructed) {
+      this.numUnitsConstructed[type]++;
+    } else {
+      this.numUnitsConstructed[type] = 1;
+    }
+  }
+
+  // Count of units built by the player, including construction
+  unitsConstructed(type: UnitType): number {
+    const built = this.numUnitsConstructed[type] ?? 0;
+    let constructing = 0;
+    for (const unit of this._units) {
+      if (unit.type() !== UnitType.Construction) continue;
+      if (unit.constructionType() !== type) continue;
+      constructing++;
+    }
+    const total = constructing + built;
+    return total;
+  }
+
+  // Count of units owned by the player, including construction
+  unitsOwned(type: UnitType): number {
+    let total = 0;
+    for (const unit of this._units) {
+      if (unit.type() === type) {
+        total++;
+        continue;
+      }
+      if (unit.type() !== UnitType.Construction) continue;
+      if (unit.constructionType() !== type) continue;
+      total++;
+    }
+    return total;
   }
 
   sharesBorderWith(other: Player | TerraNullius): boolean {
@@ -749,6 +776,7 @@ export class PlayerImpl implements Player {
       params,
     );
     this._units.push(b);
+    this.recordUnitConstructed(type);
     this.removeGold(cost);
     this.removeTroops("troops" in params ? (params.troops ?? 0) : 0);
     this.mg.addUpdate(b.toUpdate());