Use DataPool for the LarDigitCnv p2/p3

Use DataPool for the LarDigitCnv

ping @tadej and @jchapman

as this should could help with this but we need to figure how to best do the test.

 18246800 calls to allocation functions with 8.76M peak consumption from         
   483 LArDigitContainerCnv_p2::persToTrans(LArDigitContainer_p2 const*, LArDigitContainer*, MsgStream&) const
   484   at /build/atnight/localbuilds/nightlies/Athena/23.0/athena/LArCalorimeter/LArCnv/LArTPCnv/src/LArDigitContainerCnv_p2.cxx:55
   485   in /cvmfs/atlas-nightlies.cern.ch/repo/sw/23.0_Athena_x86_64-centos7-gcc11-opt/2023-06-30T2101/Athena/23.0.36/InstallArea/x86_64-centos7-gcc11-opt/lib/libLArTPCnv.so
   486 18246800 calls with 8.76M peak consumption from:                                
   487     TPConverterConstBase<>::persToTrans(LArDigitContainer_p2 const*, LArDigitContainer*, MsgStream&)

ping @ssnyder. Although the later commit does not add something in AthAllocators The line at the end seems to do the cleanup after we are done SG::ArenaHeader::defaultHeader()->allocator(0)->erase();