refactor!: use FutureOr to allow synchronous interceptors

lib/models/interceptor_contract.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:http/http.dart';
 
 ///Interceptor interface to create custom Interceptor for http.
@@ -26,11 +28,11 @@ import 'package:http/http.dart';
 ///}
 ///```
 abstract class InterceptorContract {
-  Future<bool> shouldInterceptRequest() async => true;
+  FutureOr<bool> shouldInterceptRequest() => true;
 
-  Future<BaseRequest> interceptRequest({required BaseRequest request});
+  FutureOr<BaseRequest> interceptRequest({required BaseRequest request});
 
-  Future<bool> shouldInterceptResponse() async => true;
+  FutureOr<bool> shouldInterceptResponse() => true;
 
-  Future<BaseResponse> interceptResponse({required BaseResponse response});
+  FutureOr<BaseResponse> interceptResponse({required BaseResponse response});
 }

lib/models/retry_policy.dart

@@ -36,14 +36,13 @@ import 'package:http/http.dart';
 abstract class RetryPolicy {
   /// Defines whether the request should be retried when an Exception occurs
   /// while making said request to the server.
-  Future<bool> shouldAttemptRetryOnException(
-          Exception reason, BaseRequest request) async =>
+  FutureOr<bool> shouldAttemptRetryOnException(
+          Exception reason, BaseRequest request) =>
       false;
 
   /// Defines whether the request should be retried after the request has
   /// received `response` from the server.
-  Future<bool> shouldAttemptRetryOnResponse(BaseResponse response) async =>
-      false;
+  FutureOr<bool> shouldAttemptRetryOnResponse(BaseResponse response) => false;
 
   /// Number of maximum request attempts that can be retried.
   final int maxRetryAttempts = 1;