fix(android): guard getLongVersionCode() for API < 28 to prevent launch crash

src/serious_python_android/CHANGELOG.md

@@ -1,3 +1,7 @@
+## Unreleased
+
+* Fix app crashing on launch on Android 8.1 and below (API < 28). The `getAppVersion` method-channel handler, called on every startup, used `PackageInfo.getLongVersionCode()` (API 28+) unconditionally. R8 outlines this call into a synthetic class that it can merge with other API 28+ outlines — notably Flutter 3.41's `ImageDecoder`-based image decoder — and invoking that merged class on API < 28 fails verification with `NoClassDefFoundError: android.graphics.ImageDecoder$OnHeaderDecodedListener`. The call is now guarded with a `Build.VERSION.SDK_INT` check, falling back to the deprecated `versionCode` int field on older devices.
+
 ## 4.1.0
 
 * Run the `extractAsset` / `unzipAsset` / `loadLibrary` method-channel handlers on a background `Executor` (posting the `Result` back on the main looper) instead of inline on the platform main thread. The first-launch asset unpack and the pyjnius native-library load no longer block Android's `Choreographer`, so Flutter's vsync isn't starved and on-screen animations (e.g. a boot/splash spinner) stay smooth while the app starts.

src/serious_python_android/android/src/main/java/com/flet/serious_python_android/AndroidPlugin.java

@@ -122,7 +122,16 @@ public void onMethodCall(@NonNull MethodCall call, @NonNull Result result) {
         android.content.pm.PackageManager pm = context.getPackageManager();
         android.content.pm.PackageInfo info = pm.getPackageInfo(packageName, 0);
         String versionName = info.versionName;
-        long versionCode = info.getLongVersionCode();
+        // PackageInfo.getLongVersionCode() is API 28+. Calling it unconditionally
+        // makes the Android Gradle plugin (R8) outline the call into a synthetic
+        // class that it may merge with other API 28+ outlines (e.g. Flutter's
+        // ImageDecoder-based image decoder). Invoking that merged class on
+        // API < 28 fails verification with NoClassDefFoundError and crashes the
+        // app on launch, because getAppVersion runs on every startup. Guard the
+        // call so older devices use the deprecated int field instead.
+        long versionCode = (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.P)
+            ? info.getLongVersionCode()
+            : (long) info.versionCode;
         result.success(versionName + "+" + versionCode);
       } catch (Exception e) {
         result.error("Error", e.getMessage(), null);