Adds requests for total flight time and flight in between timestamps

lib/db/db_helper.dart

@@ -160,6 +160,34 @@ class DbHelper {
     return maps.map((e) => Flight.fromMap(e)).toList();
   }
 
+  Future<List<Flight>> getFlightsBetween(
+    int startTimestamp,
+    int endTimestamp,
+  ) async {
+    final db = await database;
+    final maps = await db.rawQuery('''
+        SELECT * FROM flights AS F
+        WHERE F.start_timestamp >= $startTimestamp AND F.end_timestamp <= $endTimestamp
+    ''');
+    return maps.map((e) => Flight.fromMap(e)).toList();
+  }
+
+  Future<int?> getTotalFlightTime() async {
+    final db = await database;
+    final ft = await db.rawQuery('''
+        SELECT SUM(F.end_timestamp - F.startTimestamp) FROM flights AS F
+    ''');
+    final mapping = ft.firstOrNull;
+    if (mapping == null) {
+      return null;
+    }
+    final val = mapping["SUM(F.end_timestamp - F.startTimestamp)"];
+    if (val is! int) {
+      return null;
+    }
+    return val;
+  }
+
   Future closeDb() async {
     final db = await database;
     log.info("Closing database.");