[PWGDQ] Fill FIT variables in tableMakerMC_withAssoc

[sigurdnese]

• Optionally fill FIT variables in the MC tablemakerWithAssoc if the event fill map includes VarManager::ObjTypes::Fit.
• VarManager::FillFIT takes the FIT tables as arguments, so they are added to the fullSkimming arguments.
• Association between the BC table and FIT tables requires more tables to be joined to the BCsWithTimestamps table. Therefore, a new join MyBCs was defined, and the BC table type was upgraded to a template type in fullSkimming and skimCollisions.

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 68 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for ed434df at 2026-09-25 08:24:

## sw/BUILD/O2-latest/log
Error: missing ; at end of rule at /sw/SOURCES/O2/daily-20260923-0000/daily-20260923-0000/Detectors/TPC/base/src/TPCBaseLinkDef.h:75:56
Error: missing ; at end of rule at /sw/SOURCES/O2/daily-20260923-0000/daily-20260923-0000/Detectors/TPC/base/src/TPCBaseLinkDef.h:83:135
Error: missing ; at end of rule at /sw/SOURCES/O2/daily-20260923-0000/daily-20260923-0000/Detectors/TPC/base/src/TPCBaseLinkDef.h:84:135
Error: missing ; at end of rule at /sw/SOURCES/O2/daily-20260923-0000/daily-20260923-0000/Detectors/Upgrades/ALICE3/ECal/base/src/ECalBaseLinkDef.h:19:48
Error: missing ; at end of rule at /sw/SOURCES/O2/daily-20260923-0000/daily-20260923-0000/Detectors/Upgrades/ALICE3/RICH/base/src/RICHBaseLinkDef.h:18:48
Error: missing ; at end of rule at /sw/SOURCES/O2/daily-20260923-0000/daily-20260923-0000/Detectors/Upgrades/ALICE3/MID/base/src/MI3BaseLinkDef.h:18:47


## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 1 errors and 0 warnings.'
Found 1 errors and 0 warnings.
++ [[ 1 -gt 0 ]]
++ cat /sw/BUILD/4a52fe5760daed691228f17a1511f827aa0e3cc5/O2Physics-code-check/errors.txt
PWGDQ/TableProducer/tableMakerMC_withAssoc.cxx:760:53: error: no header providing "std::nullptr_t" is directly included [misc-include-cleaner,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 1 -gt 0 ]]
++ exit 1
--

Full log here.

[vkucera]

@sigurdnese Please remember to fix errors before merging.
@iarsene Please do not approve PRs which introduce errors.