Add debug logs; deduplicate ffi import

Move and remove duplicate ffi import, format python invalidate key assignment, and add spDebug logging for Python version and app version. These changes improve readability and add runtime debug output to help diagnose bundle extraction and versioning without altering core behavior.

Author: FeodorFitsner

src/serious_python_android/lib/serious_python_android.dart

@@ -1,10 +1,10 @@
 import 'dart:async';
 import 'dart:io';
 
+import 'package:ffi/ffi.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'package:ffi/ffi.dart';
 import 'package:path/path.dart' as p;
 import 'package:serious_python_platform_interface/serious_python_platform_interface.dart';
 
@@ -82,8 +82,10 @@ class SeriousPythonAndroid extends SeriousPythonPlatform {
       throw Exception("Python bundle not found: $bundlePath");
     }
     final pythonVersion = getPythonFullVersion();
-    final pythonInvalidateKey =
-        pythonVersion != null ? "python:$pythonVersion" : "python:$pythonSharedLib";
+    spDebug("Python version: $pythonVersion");
+    final pythonInvalidateKey = pythonVersion != null
+        ? "python:$pythonVersion"
+        : "python:$pythonSharedLib";
     var pythonLibPath = await extractFileZip(bundlePath,
         targetPath: "python_bundle", invalidateKey: pythonInvalidateKey);
     spDebug("pythonLibPath: $pythonLibPath");
@@ -99,6 +101,7 @@ class SeriousPythonAndroid extends SeriousPythonPlatform {
 
     if (await File(sitePackagesZipPath).exists()) {
       final appVersion = await getAppVersion();
+      spDebug("App version: $appVersion");
       final sitePackagesInvalidateKey =
           appVersion != null ? "app:$appVersion" : null;
       var sitePackagesPath = await extractFileZip(sitePackagesZipPath,