fix: add proguard rules, avoid protobuf generated classes got obfuscated

flutter/android/app/build.gradle

@@ -93,6 +93,7 @@ android {
             // TODO: Add your own signing config for the release build.
             // Signing with the debug keys for now, so `flutter run --release` works.
             signingConfig signingConfigs.release
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules'
         }
     }
 }

flutter/android/app/proguard-rules

@@ -0,0 +1,4 @@
+# Keep class members from protobuf generated code.
+-keepclassmembers class * extends com.google.protobuf.GeneratedMessageLite {
+  <fields>;
+}