L1: optimizations of the reconstruction time

Several improvements in the CA tracker to minimize the reconstruction time also in debug-with-mc mode:

• new subslice splitting algorithm that searches in partially disordered data
• move the split in sub-timeslices from the CbmL1 level to the tracker core
• in debug-with-Mc mode with event builder: read only those MC events that are related to the current reco event.

In addition, many cleanups. In particular, the "legacy event mode" is removed.

macro/beamtime/mcbm2021/mcbm_event_reco.C

@@ -808,7 +808,6 @@ Bool_t mcbm_event_reco(UInt_t uRunId                   = 1588,
   //   CbmKF* kalman = new CbmKF();
   //   run->AddTask(kalman);
   //   CbmL1* l1 = new CbmL1();
-  //   l1->SetLegacyEventMode(1);
   //   l1->SetMcbmMode();
   //   if (strcmp(geoSetupTag.data(), "mcbm_beam_2021_07_surveyed") == 0) l1->SetMissingHits(1);
   //