[PWGHF] Refactor mixed event handling for track selection in Charm Track femto task

[zhangbiao-phy]

Updated mixed event handling to use selected partition for track 1 based on PDG code. This change applies to multiple decay channels and ensures correct partitioning for mixed events. The effect only for the MC mixed-event

[github-actions]

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

[alibuild]

Auto-approving on behalf of @zhangbiao-phy.

[alibuild]

Error while checking build/O2Physics/code-check for b6de1a3 at 2026-07-24 15:58:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 8 errors and 0 warnings.'
Found 8 errors and 0 warnings.
++ [[ 8 -gt 0 ]]
++ cat /sw/BUILD/0790eeeea0985c198490546113f014df9a356ccc/O2Physics-code-check/errors.txt
PWGHF/HFC/Tasks/taskCharmHadronsTrackFemtoDream.cxx:385:9: error: do not use 'else' after 'return' [readability-else-after-return,-warnings-as-errors]
PWGHF/HFC/Tasks/taskCharmHadronsTrackFemtoDream.cxx:401:9: error: do not use 'else' after 'return' [readability-else-after-return,-warnings-as-errors]
PWGHF/HFC/Tasks/taskCharmHadronsTrackFemtoDream.cxx:624:132: error: the parameter 'policy' is copied for each invocation but only used as a const reference; consider making it a const reference [performance-unnecessary-value-param,-warnings-as-errors]
PWGHF/HFC/Tasks/taskCharmHadronsTrackFemtoDream.cxx:915:9: error: do not use 'else' after 'continue' [readability-else-after-return,-warnings-as-errors]
PWGHF/HFC/Tasks/taskCharmHadronsTrackFemtoDream.cxx:961:9: error: do not use 'else' after 'continue' [readability-else-after-return,-warnings-as-errors]
PWGHF/HFC/Tasks/taskCharmHadronsTrackFemtoDream.cxx:1006:9: error: do not use 'else' after 'continue' [readability-else-after-return,-warnings-as-errors]
PWGHF/HFC/Tasks/taskCharmHadronsTrackFemtoDream.cxx:1051:9: error: do not use 'else' after 'continue' [readability-else-after-return,-warnings-as-errors]
PWGHF/HFC/Tasks/taskCharmHadronsTrackFemtoDream.cxx:1094:9: error: do not use 'else' after 'continue' [readability-else-after-return,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 8 -gt 0 ]]
++ exit 1
--

Full log here.

[vkucera]

@zhangbiao-phy Please fix the errors.

[zhangbiao-phy]

@zhangbiao-phy Please fix the errors.

Thanks for reminding me!

[alibuild]

Auto-approving on behalf of @zhangbiao-phy.