[PWGUD] Add deuteron in UPC task

[m-rasa]

Add new task for the study of deuteron production in UPC collisions.
CMakeList file modified to include the new task.

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 47 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for 19685df at 2026-10-04 21:22:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 1 errors and 2 warnings.'
Found 1 errors and 2 warnings.
++ [[ 1 -gt 0 ]]
++ cat /sw/BUILD/3642724a42d20fb3d6ef032a3d1ce6f1b67a7f87/O2Physics-code-check/errors.txt
PWGUD/Tasks/sgDeuteronSpectra.cxx:110:24: error: no header providing "TMath::Abs" is directly included [misc-include-cleaner,-warnings-as-errors]
++ [[ 2 -gt 0 ]]
++ cat /sw/BUILD/3642724a42d20fb3d6ef032a3d1ce6f1b67a7f87/O2Physics-code-check/warnings.txt
PWGUD/Tasks/sgDeuteronSpectra.cxx:98:5: warning: do not declare C-style arrays, use 'std::array' instead [modernize-avoid-c-arrays]
PWGUD/Tasks/sgDeuteronSpectra.cxx:105:11: warning: implicit conversion 'int' -> 'bool' [readability-implicit-bool-conversion]
++ [[ 1 -gt 0 ]]
++ exit 1
--

Full log here.

[alibuild]

Error while checking build/O2Physics/o2 for 8f0839d at 2026-10-05 10:17:

No log files found

Full log here.

[alibuild]

Error while checking build/O2Physics/code-check for 8f0839d at 2026-10-05 14:15:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 2 errors and 0 warnings.'
Found 2 errors and 0 warnings.
++ [[ 2 -gt 0 ]]
++ cat /sw/BUILD/6837c2288adb0735d5f1240e842d7b97ec169de0/O2Physics-code-check/errors.txt
PWGUD/Tasks/sgDeuteronSpectra.cxx:28:1: error: included header TMath.h is not used directly [misc-include-cleaner,-warnings-as-errors]
PWGUD/Tasks/sgDeuteronSpectra.cxx:112:24: error: no header providing "TMath::Abs" is directly included [misc-include-cleaner,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 2 -gt 0 ]]
++ exit 1
--

Full log here.

[vkucera]

@m-rasa Please fix the errors before merging.

[m-rasa]

@vkucera working on it.
The code checker was a real error (fixed now), while the O2 error was due to an outage of git host.

[vkucera]

@m-rasa Thanks for fixing the error. However, you seem to include a ROOT header to use TMath::Abs which is completely unnecessary because O2 works with native C++ types and therefore you should use std::abs instead, as recommended by the root/entity warning in O2 linter.
Since you are adding a new file, I would strongly recommend to implement the suggestions from the O2 linter warnings, since they point to several issues in your code which should not go unnoticed.

[m-rasa]

@vkucera thanks for the suggestion.
I was in the impression that, since the O2linter check were ok, everything was good. Will look on the warnings on the O2 linter and implement them. Thanks!
Hence, moving back to draft the PR.

[vkucera]

@vkucera thanks for the suggestion. I was in the impression that, since the O2linter check were ok, everything was good. Will look on the warnings on the O2 linter and implement them. Thanks! Hence, moving back to draft the PR.

Thank you.
Currently, O2 linter check fails only when new errors are found which is now constrained only to a few categories which are completely clean in the whole repository. The rest has to be reported as warnings because of the pre-existing issues.
Since you are adding a new file, all the issues reported by CI checks are new, so it is highly encouraged to fix them before merging the new code in the upstream repository.