Keep the Cave chunk-seeding counters in members

This moves the two counters of Cave::BeginPrimary out of function-local statics, like the detector stepping state.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: sawenzel

Detectors/Passive/include/DetectorsPassive/Cave.h

@@ -77,6 +77,8 @@ class Cave : public FairDetector
 
   bool mHasZDC = true;  //! flag indicating if ZDC will be included
   bool mHasRB24 = true; //! flag indicating if RB24 will be included
+  int mPrimaryCounter = 0;   //! primaries started, for the internal chunk seeding
+  int mChunkSeedCounter = 1; //! next seed index of the internal chunk seeding
   ClassDefOverride(o2::passive::Cave, 1);
 };
 } // namespace passive

Detectors/Passive/src/Cave.cxx

@@ -146,22 +146,19 @@ void Cave::FinishPrimary()
 // setting
 void Cave::BeginPrimary()
 {
-  static int primcounter = 0;
-
   // only do it, if not in pure trackSeeding mode
   if (!o2::conf::SimCutParams::Instance().trackSeed) {
     auto& conf = o2::conf::SimConfig::Instance();
     auto chunks = conf.getInternalChunkSize();
     if (chunks != -1) {
-      if (primcounter % chunks == 0) {
-        static int counter = 1;
-        auto seed = counter + 10;
+      if (mPrimaryCounter % chunks == 0) {
+        auto seed = mChunkSeedCounter + 10;
         gRandom->SetSeed(seed);
-        counter++;
+        mChunkSeedCounter++;
       }
     }
   }
-  primcounter++;
+  mPrimaryCounter++;
 }
 
 bool Cave::ProcessHits(FairVolume*)