[PWGUD] preslice particles

[miedema-11]

No description provided.

[github-actions]

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

[alibuild]

Error while checking build/O2Physics/o2 for 8a0ce6e at 2026-04-15 09:39:

## sw/BUILD/O2Physics-latest/log
/sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0/PWGUD/Tasks/flowMcUpc.cxx:127:67: error: expected primary-expression before '<' token
/sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0/PWGUD/Tasks/flowMcUpc.cxx:127:75: error: expected primary-expression before '>' token
/sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0/PWGUD/Tasks/flowMcUpc.cxx:172:64: error: expected primary-expression before '<' token
/sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0/PWGUD/Tasks/flowMcUpc.cxx:172:72: error: expected primary-expression before '>' token
ninja: build stopped: subcommand failed.

Full log here.