feat: add subtitle seek keyboard shortcuts

close #236

lib/services/keyboard_shortcuts_service.dart

@@ -318,6 +318,12 @@ class KeyboardShortcutsService {
         player.setRate(1.0);
         _settingsService.setDefaultPlaybackSpeed(1.0);
         break;
+      case 'sub_seek_next':
+        player.command(['sub-seek', '1']);
+        break;
+      case 'sub_seek_prev':
+        player.command(['sub-seek', '-1']);
+        break;
     }
   }
 
@@ -358,6 +364,10 @@ class KeyboardShortcutsService {
         return 'Decrease Speed';
       case 'speed_reset':
         return 'Reset Speed';
+      case 'sub_seek_next':
+        return 'Seek to Next Subtitle';
+      case 'sub_seek_prev':
+        return 'Seek to Previous Subtitle';
       default:
         return action;
     }

lib/services/settings_service.dart

@@ -353,6 +353,8 @@ class SettingsService extends BaseSharedPreferencesService {
       'speed_increase': 'Plus',
       'speed_decrease': 'Minus',
       'speed_reset': 'R',
+      'sub_seek_next': 'Ctrl+Right',
+      'sub_seek_prev': 'Ctrl+Left',
     };
   }
 
@@ -376,6 +378,8 @@ class SettingsService extends BaseSharedPreferencesService {
       'speed_increase': HotKey(key: PhysicalKeyboardKey.equal),
       'speed_decrease': HotKey(key: PhysicalKeyboardKey.minus),
       'speed_reset': HotKey(key: PhysicalKeyboardKey.keyR),
+      'sub_seek_next': HotKey(key: PhysicalKeyboardKey.arrowRight, modifiers: [HotKeyModifier.control]),
+      'sub_seek_prev': HotKey(key: PhysicalKeyboardKey.arrowLeft, modifiers: [HotKeyModifier.control]),
     };
   }