Removal of api key

Network calls,
integration of retrofit api
added backup api

lib/data/network/backupCurrencyApi.dart

@@ -0,0 +1,35 @@
+import 'package:dio/dio.dart';
+import 'package:json_annotation/json_annotation.dart';
+import 'package:retrofit/retrofit.dart';
+
+import '../model/Currency.dart';
+
+part 'backupCurrencyApi.g.dart';
+
+@RestApi(baseUrl: "https://api.frankfurter.app/")
+abstract class BackupCurrencyApi {
+  factory BackupCurrencyApi(Dio dio, {String baseUrl}) = _BackupCurrencyApi;
+
+  @GET("latest?")
+  Future<HttpResponse<CurrencyResponse>> getCurrencyRate(@Query("from") String currencyFrom,
+      @Query("to") String currencyTo);
+}
+
+@JsonSerializable()
+class CurrencyResponse implements Mapper{
+  String? data;
+  double amount;
+  Map<String, double>? rates;
+  String? base;
+
+  CurrencyResponse(this.data, this.amount, this.rates, this.base);
+
+  factory CurrencyResponse.fromJson(Map<String, dynamic> json) => _$CurrencyResponseFromJson(json);
+  Map<String, dynamic> toJson() => _$CurrencyResponseToJson(this);
+
+  @override
+  Currency convert() {
+    MapEntry<String, double>? entry = rates?.entries.elementAt(0);
+    return Currency(base, entry?.key, entry?.value);
+  }
+}