Enhance tender estimated value resolution and add unit tests

- Updated the `ResolvedEstimatedValueAndCurrency` method to aggregate procurement lot values when the tender-level estimated value is not set, improving accuracy in value retrieval.
- Introduced the `AggregateProcurementLotEstimatedValue` function to sum estimated values from procurement lots and return the first found currency.
- Modified the `ToResponseWithLanguage` method to utilize the new estimated value resolution logic.
- Added unit tests for the new functionality, ensuring correct behavior for various scenarios in the `entity_test.go` and `budget_test.go` files.

This update improves the handling of estimated values in tenders, enhancing the overall reliability of the tender management system.

ted/budget_test.go

@@ -0,0 +1,58 @@
+package ted
+
+import "testing"
+
+func TestCurrencyTextAmountAndCurrency(t *testing.T) {
+	t.Run("chardata", func(t *testing.T) {
+		amount, currency := (CurrencyText{CurrencyID: "EUR", Text: "1 234,56"}).AmountAndCurrency()
+		if amount != "1 234,56" {
+			t.Fatalf("unexpected amount %q", amount)
+		}
+		if currency != "EUR" {
+			t.Fatalf("unexpected currency %q", currency)
+		}
+	})
+
+	t.Run("value child", func(t *testing.T) {
+		amount, currency := (CurrencyText{CurrencyID: "EUR", Value: "500000"}).AmountAndCurrency()
+		if amount != "500000" {
+			t.Fatalf("unexpected amount %q", amount)
+		}
+		if currency != "EUR" {
+			t.Fatalf("unexpected currency %q", currency)
+		}
+	})
+}
+
+func TestContractNoticeGetBudgetSumsAllLots(t *testing.T) {
+	cn := ContractNotice{
+		ProcurementProjectLots: []ProcurementProjectLot{
+			{
+				ProcurementProject: &ProcurementProject{
+					RequestedTenderTotal: &RequestedTenderTotal{
+						EstimatedOverallContractAmount: CurrencyText{CurrencyID: "EUR", Text: "100000"},
+					},
+				},
+			},
+			{
+				ProcurementProject: &ProcurementProject{
+					RequestedTenderTotal: &RequestedTenderTotal{
+						EstimatedOverallContractAmount: CurrencyText{CurrencyID: "EUR", Text: "250000"},
+					},
+				},
+			},
+		},
+	}
+
+	amount, currency := cn.GetBudget()
+	value, ok := ParseEuropeanAmount(amount)
+	if !ok {
+		t.Fatalf("failed to parse budget amount %q", amount)
+	}
+	if value != 350000 {
+		t.Fatalf("expected 350000, got %v", value)
+	}
+	if currency != "EUR" {
+		t.Fatalf("expected EUR, got %q", currency)
+	}
+}