Ensure single CPython interpreter per process

Introduces a _pythonInitialized flag to prevent repeated initialization and finalization of the CPython interpreter, addressing crashes on second launch with CPython 3.12. Py_Finalize is now commented out to maintain interpreter stability.

Author: FeodorFitsner

src/serious_python_android/lib/src/cpython.dart

@@ -11,6 +11,9 @@ import 'gen.dart';
 export 'gen.dart';
 
 CPython? _cpython;
+// Keep a single interpreter per process; repeated init/finalize of CPython 3.12
+// from an embedder is fragile and was crashing on second launch.
+bool _pythonInitialized = false;
 
 CPython getCPython(String dynamicLibPath) {
   return _cpython ??= _cpython = CPython(DynamicLibrary.open(dynamicLibPath));
@@ -51,8 +54,13 @@ Future<String> runPythonProgramInIsolate(List<Object> arguments) async {
   debugPrint("programModuleName: $programModuleName");
 
   final cpython = getCPython(dynamicLibPath);
-  cpython.Py_Initialize();
-  debugPrint("after Py_Initialize()");
+  if (!_pythonInitialized) {
+    cpython.Py_Initialize();
+    _pythonInitialized = true;
+    debugPrint("after Py_Initialize()");
+  } else {
+    debugPrint("Python already initialized; reusing interpreter");
+  }
 
   var result = "";
 
@@ -75,8 +83,8 @@ Future<String> runPythonProgramInIsolate(List<Object> arguments) async {
     malloc.free(moduleNamePtr);
   }
 
-  cpython.Py_Finalize();
-  debugPrint("after Py_Finalize()");
+  // cpython.Py_Finalize();
+  // debugPrint("after Py_Finalize()");
 
   sendPort.send(result);