[PWGLF] Correcting the invariant mass calulation of generated Delta particles and adding the mass axis in histograms for generated particles.

[bhattdurgesh921-sys]

Hi @dmallick2,

In this PR, we corrected the method used to calculate the invariant mass of the generated Δ particles. Previously, the invariant mass was reconstructed from the summed four-momenta of the decay daughters, which could shift the peak from the expected resonance mass. The updated implementation now fills the generated-particle histograms directly using the generated resonance mass.
Additionally, we introduced a mass axis for the generated Δ histograms. This allows us to verify that the generated resonance mass distribution is centered at the expected PDG value and provides a useful QA check for the generated particles.

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 4 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for 7b8c7da at 2026-07-20 11:29:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 18 errors and 67 warnings.'
Found 18 errors and 67 warnings.
++ [[ 18 -gt 0 ]]
++ cat /sw/BUILD/e702c52c0ea86c2694d38fcb70c3293c28473fb5/O2Physics-code-check/errors.txt
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:160:39: error: initializer for member 'mProtonTPCMomBins' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:161:40: error: initializer for member 'mProtonTPCNSigCuts' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:162:39: error: initializer for member 'mProtonTOFMomBins' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:163:40: error: initializer for member 'mProtonTOFNSigCuts' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:164:37: error: initializer for member 'mPionTPCMomBins' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:165:38: error: initializer for member 'mPionTPCNSigCuts' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:166:37: error: initializer for member 'mPionTOFMomBins' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:167:38: error: initializer for member 'mPionTOFNSigCuts' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:168:39: error: initializer for member 'mProtonDCAPtEdges' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:169:37: error: initializer for member 'mProtonMaxDCAxy' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:170:37: error: initializer for member 'mPionDCAPtEdges' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:171:35: error: initializer for member 'mPionMaxDCAxy' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:520:11: error: use auto when initializing with a cast to avoid duplicating the type name [modernize-use-auto,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:589:11: error: use auto when initializing with a cast to avoid duplicating the type name [modernize-use-auto,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:843:13: error: variable 'rotAngle' is not initialized [cppcoreguidelines-init-variables,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:919:7: error: uninitialized record type: 'cand' [cppcoreguidelines-pro-type-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:1027:42: error: initializer for member 'mProtonPool' is redundant [readability-redundant-member-init,-warnings-as-errors]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:1028:40: error: initializer for member 'mPionPool' is redundant [readability-redundant-member-init,-warnings-as-errors]
++ [[ 67 -gt 0 ]]
++ cat /sw/BUILD/e702c52c0ea86c2694d38fcb70c3293c28473fb5/O2Physics-code-check/warnings.txt
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:425:27: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:427:51: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:431:58: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:435:48: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:453:45: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:455:57: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:457:50: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:459:59: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:461:94: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:463:47: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:465:47: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:467:56: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:469:64: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:471:58: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:526:54: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:535:59: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:537:102: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:563:54: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:594:52: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:603:57: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:605:100: warning: statement should be inside braces [readability-braces-around-statements]
PWGLF/Tasks/Resonances/deltaAnalysis.cxx:631:52: warning: statement should be inside braces [readability-braces-around-statements]
[0 more errors; see full log]

Full log here.