Finish detector events before sending hits in parallel o2-sim

This fixes the order in which a parallel o2-sim worker finalizes and sends the hits of an event.

- Detectors ran FinishEvent after SendData, while serial o2-sim (FairMCApplication) runs it before filling the output.
- TRD sorts its hits in FinishEvent, and PHOS and CPV sort them and sum duplicates.
- With TMessage transport their hits were written unsorted and, for PHOS and CPV, with duplicates.
- With shared memory the merger read the buffers while the worker rewrote them, so TRD output differed between the two transports.
- FinishEvent now runs for all detectors before SendData, and EndOfEvent after it.

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

Author: sawenzel

Steer/include/Steer/O2MCApplication.h

@@ -53,13 +53,17 @@ class O2MCApplication : public O2MCApplicationBase
 
     finishEventCommon();
 
+    // detectors finalize their hits (e.g. sorting, summing duplicates) before these are sent
+    for (auto det : listActiveDetectors) {
+      det->FinishEvent();
+    }
+
     // This special finish event version does not fill the output tree of FairRootManager
     // but forwards the data to the HitMerger
     SendData();
 
     // call end of event on active detectors
     for (auto det : listActiveDetectors) {
-      det->FinishEvent();
       det->EndOfEvent();
     }
     fStack->Reset();