Added Cyr2Lat compression by replacing 2-byte cyrillic chars by 1-byte latin

lib/helpers/cyr2lat.dart

@@ -0,0 +1,63 @@
+class Cyr2Lat {
+  static Map<String, String> _charMap = {
+    'А': 'A',
+    'В': 'B',
+    'Е': 'E',
+    'Ё': 'E',
+    'З': '3',
+    'К': 'K',
+    'М': 'M',
+    'Н': 'H',
+    'О': 'O',
+    'Р': 'P',
+    'С': 'C',
+    'Т': 'T',
+    'Х': 'X',
+    'Ь': 'b',
+    'а': 'a',
+    'е': 'e',
+    'ё': 'e',
+    'о': 'o',
+    'р': 'p',
+    'с': 'c',
+    'у': 'y',
+    'х': 'x',
+  };
+
+  static final RegExp _prefixRegExp = RegExp(r'\@\[[\S\s]+\] ');
+
+  static void setCharMap(Map<String, String> charMap) {
+    _charMap = Map.from(charMap);
+  }
+
+  static String encode(String text) {
+    if (text.isEmpty) return text;
+    final buffer = StringBuffer();
+
+    final senderName = extractSenderName(text);
+    final msgText = removeSenderName(text);
+
+    for (final rune in msgText.runes) {
+      final char = String.fromCharCode(rune);
+      buffer.write(_charMap[char] ?? char);
+    }
+
+    return senderName + buffer.toString();
+  }
+
+  static String removeSenderName(String text) {
+    final match = _prefixRegExp.matchAsPrefix(text);
+    if (match != null) {
+      return text.substring(match.end);
+    }
+    return text;
+  }
+
+  static String extractSenderName(String text) {
+    final match = _prefixRegExp.matchAsPrefix(text);
+    if (match != null) {
+      return match.group(0) ?? '';
+    }
+    return '';
+  }
+}