feat: proxy (Tor/SOCKS5) support: add optional proxy parameter

lib/src/core/client/impl/tezart_client.dart

@@ -23,7 +23,8 @@ class TezartClient {
   final RpcInterface rpcInterface;
 
   /// Default constructor.
-  TezartClient(String url) : rpcInterface = RpcInterface(url);
+  TezartClient(String url, {String? proxy})
+      : rpcInterface = RpcInterface(url, proxy: proxy);
 
   /// Returns an [OperationsList] containing a [TransactionOperation] that transfers [amount] from [source]
   /// to [destination] and returns the operation group id.\

lib/src/core/rpc/impl/rpc_interface.dart

@@ -17,7 +17,8 @@ class RpcInterface {
   final TezartHttpClient httpClient;
   final log = Logger('RpcInterface');
 
-  RpcInterface(String url) : httpClient = TezartHttpClient(url);
+  RpcInterface(String url, {String? proxy})
+      : httpClient = TezartHttpClient(url, proxy: proxy);
 
   /// Returns the block's hash of [chain] and [level]
   Future<String> branch([chain = 'main', level = 'head']) async {

lib/src/core/rpc/impl/tezart_http_client.dart

@@ -1,5 +1,6 @@
 import 'dart:io';
 
+import 'package:dio/adapter.dart';
 import 'package:dio/dio.dart' as http_client;
 import 'package:pretty_dio_logger/pretty_dio_logger.dart';
 import 'package:logging/logging.dart';
@@ -13,26 +14,36 @@ class TezartHttpClient {
   final String url;
 
   // Add client as optional parameter for testing
-  TezartHttpClient(this.url, {http_client.Dio? client}) {
+  TezartHttpClient(this.url, {http_client.Dio? client, String? proxy}) {
     // ensure that the url ends with '/' (double / is ok)
     final baseUrl = '$url/';
 
     if (client != null) {
       this.client = client;
       this.client.options.baseUrl = baseUrl;
-      return;
-    }
+    } else {
+      var options = http_client.BaseOptions(
+          baseUrl: baseUrl, contentType: 'application/json');
+
+      this.client = http_client.Dio(options);
+      this.client.interceptors.add(PrettyDioLogger(
+            logPrint: log.finest,
+            requestHeader: true,
+            requestBody: true,
+            responseBody: true,
+            responseHeader: false,
+            compact: false,
+          ));
 
-    final options = http_client.BaseOptions(baseUrl: baseUrl, contentType: 'application/json');
-    this.client = http_client.Dio(options);
-    this.client.interceptors.add(PrettyDioLogger(
-          logPrint: log.finest,
-          requestHeader: true,
-          requestBody: true,
-          responseBody: true,
-          responseHeader: false,
-          compact: false,
-        ));
+      if (proxy != null) {
+        this.client.httpClientAdapter = DefaultHttpClientAdapter()
+          ..onHttpClientCreate = (HttpClient httpClient) {
+            httpClient.findProxy = (_) => 'PROXY $proxy';
+            // Ignore SSL errors if required for development with self-signed certificates
+            httpClient.badCertificateCallback = (cert, host, port) => true;
+          };
+      }
+    }
   }
 
   Future<http_client.Response> post(String path, {dynamic data}) {