BillingData: Implement WG Master parsing

Tests/Helpers/BillingDataTest.cs

@@ -301,5 +301,49 @@ namespace Tests.Helpers {
                 TestCalcKmw(data, "WRS", 17.0, 0.95m, geb: true);
             });
         }
+
+        [Test]
+        public void Test_08_WgMaster() {
+            var data = BillingData.FromJson("""
+                {
+                  "mode": "wgmaster",
+                  "Grundbetrag": 0.033,
+                  "GBZS": 0.0,
+                  "Ausgabefaktor": 1.0,
+                  "Rebelzuschlag": 0.0,
+                  "AufschlagVolllieferanten": 0.0,
+                  "AuszahlungSorten": {
+                    "BL/": 0.097,
+                    "BP/": 0.097,
+                    "GV/K": "curve:1",
+                    "SL/": 0.097,
+                    "ZW/": 0.097,
+                    "default": "curve:0"
+                  },
+                  "AuszahlungSortenQualitätsstufe": {
+                    "WEI": 0.005
+                  },
+                  "Kurven": [{
+                    "id": 0,
+                    "mode": "oe",
+                    "data": 0.033,
+                    "geb": 0
+                  }, {
+                    "id": 1,
+                    "mode": "oe",
+                    "data": {
+                      "88oe": 0.032,
+                      "89oe": 0.065
+                    }
+                  }]
+                }
+                """, AttributeVariants);
+            Assert.Multiple(() => {
+                TestCalcOe(data, "GVK", 73, 0.032m);
+                TestCalcOe(data, "ZWS", 74, 0.033m);
+                TestCalcOe(data, "GV", 75, 0.005m, qualid: "WEI");
+                TestCalcOe(data, "GVK", 115, 0.065m);
+            });
+        }
     }
 }