feat(protocol): add FTP, FTPS and FTPES downloads (#1569)

ui/flutter/test/api/downloader_config_test.dart

@@ -67,6 +67,25 @@ void main() {
     expect(decoded.disablePex, isTrue);
   });
 
+  test('FTP settings round-trip with the Go json keys', () {
+    final config = DownloaderConfig();
+    config.protocolConfig.ftp.connections = 6;
+
+    final json = config.toJson();
+    final ftp = (json['protocolConfig'] as Map<String, dynamic>)['ftp'] as Map<String, dynamic>;
+    expect(ftp, {'connections': 6});
+    expect(DownloaderConfig.fromJson(json).protocolConfig.ftp.connections, 6);
+  });
+
+  test('a stored config without FTP settings still parses', () {
+    final json = DownloaderConfig().toJson();
+    (json['protocolConfig'] as Map<String, dynamic>).remove('ftp');
+
+    final decoded = DownloaderConfig.fromJson(json);
+    expect(decoded.protocolConfig.ftp.connections, 0);
+    expect(decoded.protocolConfig.http.connections, DownloaderConfig().protocolConfig.http.connections);
+  });
+
   test('BitTorrent peer discovery stays on when a stored config lacks the keys', () {
     final bt = BtConfig.fromJson({'listenPort': 6881, 'seedRatio': 1.0});
     expect(bt.disableDht, isFalse);

ui/flutter/test/api/task_stats_test.dart

@@ -23,6 +23,22 @@ void main() {
     expect(stats.connections.last.completed, isTrue);
   });
 
+  test('FTP stats use the HTTP connection layout', () {
+    final stats =
+        TaskStats.fromJson(Protocol.ftp, {
+              'snapshot': {
+                'connections': [
+                  {'downloaded': 512, 'total': 1024, 'completed': false, 'failed': false, 'retryTimes': 1},
+                ],
+              },
+              'runtime': null,
+            })
+            as HttpTaskStats;
+
+    expect(stats.connections.single.downloaded, 512);
+    expect(stats.connections.single.retryTimes, 1);
+  });
+
   test('BT stats decode the ordered completion bitset and peer transport', () {
     final stats =
         TaskStats.fromJson(Protocol.bt, {