[PWGLF] Update event selection, cuts, and histograms for analysis

[PaolaVT]

Update event selection, cuts, and histograms for analysis

[github-actions]

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

[alibuild]

Error while checking build/O2Physics/o2 for 4dea103 at 2026-04-09 10:30:

## sw/BUILD/O2Physics-latest/log
/sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0/PWGLF/Tasks/Nuspex/multiplicityPt.cxx:638:16: error: comparison of integer expressions of different signedness: 'size_t' {aka 'long unsigned int'} and 'int64_t' {aka 'long int'} [-Werror=sign-compare]
/sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0/PWGLF/Tasks/Nuspex/multiplicityPt.cxx:647:15: error: comparison of integer expressions of different signedness: 'size_t' {aka 'long unsigned int'} and 'int64_t' {aka 'long int'} [-Werror=sign-compare]
ninja: build stopped: subcommand failed.

Full log here.