Prevent multiple Python interpreter initializations

Adds a check to skip starting a new Python interpreter if one is already running. Returns a message to the caller and logs the event when initialization is skipped.

Author: FeodorFitsner

src/serious_python_android/lib/src/cpython.dart

@@ -122,7 +122,12 @@ Future<String> runPythonProgramInIsolate(List<Object> arguments) async {
     cpython.Py_Initialize();
     _pyLog("after Py_Initialize()");
   } else {
-    _pyLog("Python already initialized; reusing interpreter");
+    // Interpreter is already running; skip launching another run and let the
+    // previously started script continue. Return a message for the caller.
+    _pyLog("Python already initialized; skipping new run");
+    final msg = "Python already initialized; skipped starting a new run.";
+    sendPort.send(msg);
+    return msg;
   }
 
   var result = "";