[15.0.X] miscellaneous improvements to HLTriggerOffline/Scouting plugins

[mmusich]

backport of #47471

PR description:

This is a follow-up to #47235.
Title says it all:

• merge header file within implementation (as recommended for cmssw plugins);
• modernize / simplify code;
• remove duplication of similar functions in a single utility header file;
• do not pass const objects by value, but by const reference;
• fix broken fillDescriptions methods;

PR validation:

runTheMatrix.py -l 145.415 -t 4 -j 8 runs fine.

If this PR is a backport please specify the original PR and why you need to backport that PR. If this PR will be backported please specify to which release cycle the backport is meant for:

verbatim backport of #47471 to the 2025 data-taking release.

[cmsbuild]

A new Pull Request was created by @mmusich for CMSSW_15_0_X.

It involves the following packages:

• HLTriggerOffline/Scouting (dqm)

@antoniovagnerini, @cmsbuild, @rseidita can you please review it and eventually sign? Thanks.
@missirol, @mtosi this is something you requested to watch as well.
@antoniovilela, @mandrenguyen, @rappoccio, @sextonkennedy you are the release manager for this.

cms-bot commands are listed here

• Backported from miscellaneous improvements to HLTriggerOffline/Scouting plugins #47471

[cmsbuild]

cms-bot internal usage

[mmusich]

test parameters:

• workflow = 145.415

[mmusich]

@cmsbuild, please test

[cmsbuild]

+1

Size: This PR adds an extra 16KB to repository
Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-f7d3d1/44871/summary.html
COMMIT: 06da71c
CMSSW: CMSSW_15_0_X_2025-03-09-0000/el8_amd64_gcc12
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmssw/47541/44871/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• You potentially removed 1 lines from the logs
• Reco comparison results: 0 differences found in the comparisons
• DQMHistoTests: Total files compared: 51
• DQMHistoTests: Total histograms compared: 4113162
• DQMHistoTests: Total failures: 45
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 4113097
• DQMHistoTests: Total skipped: 20
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 50 files compared)
• Checked 221 log files, 193 edm output root files, 51 DQM output files
• TriggerResults: no differences found

[antoniovagnerini]

+dqm

• spurious differences seen from unstable WF 12834.7 (open issue spurious differences in outputs of Run-3 wfs *.7 #39803 )

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_15_0_X IBs (tests are also fine) and once validation in the development release cycle CMSSW_15_1_X is complete. This pull request will now be reviewed by the release team before it's merged. @antoniovilela, @sextonkennedy, @rappoccio, @mandrenguyen (and backports should be raised in the release meeting by the corresponding L2)