feat: Adding forgotten factory files

src/main/java/millions/model/factories/PurchaseFactory.java

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+package millions.model.factories;
+
+import millions.model.Purchase;
+import millions.model.Share;
+
+public class PurchaseFactory extends TransactionFactory {
+  public Purchase createTransaction(Share share, int week) {
+    return new Purchase(share, week);
+  }
+}

src/main/java/millions/model/factories/SaleFactory.java

@@ -0,0 +1,10 @@
+package millions.model.factories;
+
+import millions.model.Sale;
+import millions.model.Share;
+
+public class SaleFactory extends TransactionFactory {
+  public Sale createTransaction(Share share, int week) {
+    return new Sale(share, week);
+  }
+}

src/main/java/millions/model/factories/TransactionFactory.java

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+package millions.model.factories;
+
+import millions.model.Share;
+import millions.model.Transaction;
+
+public abstract class TransactionFactory {
+  public abstract Transaction createTransaction(Share share, int week);
+}