[PWGEM] Add checkMCPairTemplate.cxx as task to study shape of different b->Hc->e decays

[feisenhu]

Similar to checkMCTemplate, this task is used to study the systematic difference between different non-prompt open charm decays.
While checkMCTemplate studies the effect on single electron DCA, this task focuses on the pair level.
(Based on DileptonMC.h task with reduced dimensions of the hs)

[alibuild]

Error while checking build/O2Physics/o2 for 78fe773 at 2026-02-03 14:59:

## sw/BUILD/O2Physics-latest/log
CMake Error at cmake/O2PhysicsAddExecutable.cmake:135 (target_link_libraries):

Full log here.

[alibuild]

Error while checking build/O2Physics/o2 for 4e8f5c4 at 2026-02-03 17:18:

## sw/BUILD/O2Physics-latest/log
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:25:10: fatal error: PWGEM/Dilepton/Utils/PDGCodeConverter.h: No such file or directory
ninja: build stopped: subcommand failed.

Full log here.

[alibuild]

Error while checking build/O2Physics/o2 for c488f7a at 2026-02-03 19:59:

## sw/BUILD/O2Physics-latest/log
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:64:50: error: 'pdgcodeconverterutil' is not a namespace-name
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:1993:11: error: unused variable 'deta' [-Werror=unused-variable]
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:2016:11: error: unused variable 'aco' [-Werror=unused-variable]
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:2017:11: error: unused variable 'asym' [-Werror=unused-variable]
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:2031:11: error: unused variable 'quadmom' [-Werror=unused-variable]
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:1993:11: error: unused variable 'deta' [-Werror=unused-variable]
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:2016:11: error: unused variable 'aco' [-Werror=unused-variable]
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:2017:11: error: unused variable 'asym' [-Werror=unused-variable]
/sw/SOURCES/O2Physics/14779-slc9_x86-64/0/PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx:2031:11: error: unused variable 'quadmom' [-Werror=unused-variable]
ninja: build stopped: subcommand failed.

Full log here.