[PWGEM] Fix TTCA weights when using cfgRequireTrueAssociation in PWGEM/Dilepton tasks

[feisenhu]

When cfgRequireTrueAssociation = true, tracks/pairs failing the MC collision association check were correctly rejected during histogram filling, but still counted in the TTCA weight denominator — causing weights of 1/N instead of 1/1 and under-filled histograms.

Affected files

• PWGEM/Dilepton/Core/SingleTrackQCMC.h — fillTrackWeightMap(): missing check for both electron and muon loops
• PWGEM/Dilepton/Core/DileptonMC.h — fillPairWeightMap(): missing check for ULS, LS++, and LS-- combination loops
• PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx — fillPairWeightMap(): same as above

Fix

Added cfgRequireTrueAssociation guard in each weight-building loop to mirror the filter already applied at fill time:

// fillPairWeightMap — now consistent with fillPairInfo
if (cfgRequireTrueAssociation &&
    (mcpos.emmceventId() != collision.emmceventId() ||
     mcneg.emmceventId() != collision.emmceventId())) {
  continue;  // skip pairs that would be rejected at fill time
}

This ensures only tracks/pairs that actually enter histograms are counted in N, keeping weight = 1/N correct under all configurations.

[github-actions]

O2 linter results: ❌ 631 errors, ⚠️ 611 warnings, 🔕 0 disabled

[Copilot]

Pull request overview

Fixes TTCA (1/N) weight normalization when cfgRequireTrueAssociation=true by ensuring tracks/pairs that would be rejected during histogram filling are also excluded from the TTCA denominator during weight-map construction.

Changes:

• Add cfgRequireTrueAssociation event-association guards in single-track TTCA weight map building (dielectron and dimuon paths).
• Add the same guard in dilepton TTCA pair weight map building for ULS, LS++, and LS-- loops.
• Mirror the above fix in the checkMCPairTemplate task’s pair weight-map construction.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
PWGEM/Dilepton/Tasks/checkMCPairTemplate.cxx	Skips MC-event-mismatched pairs during TTCA weight-map building when true association is required.
PWGEM/Dilepton/Core/SingleTrackQCMC.h	Skips MC-event-mismatched tracks during TTCA weight-map building when true association is required.
PWGEM/Dilepton/Core/DileptonMC.h	Skips MC-event-mismatched pairs during TTCA weight-map building (ULS/LS++/LS--) when true association is required.

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[alibuild]

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