[PWGCF] Add cuts counter and experimental eta gap

[meiALICE]

Add sequential cuts counter.

Add eta gap.

[github-actions]

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

[alibuild]

Error while checking build/O2Physics/code-check for cceea60 at 2026-10-17 18:30:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'To reproduce the results below locally, run: '\''aliBuild build O2Physics-code-check -e ALIBUILD_BASE_HASH=upstream/master'\''.'
To reproduce the results below locally, run: 'aliBuild build O2Physics-code-check -e ALIBUILD_BASE_HASH=upstream/master'.
++ echo 'To apply all automatic fixes, add the '\''-e O2PHYSICS_CHECKER_FIX=1'\'' option.'
To apply all automatic fixes, add the '-e O2PHYSICS_CHECKER_FIX=1' option.
++ echo 'See the documentation for more details at: <https://aliceo2group.github.io/analysis-framework/docs/tools/#running-with-o2physics-code-check>.'
See the documentation for more details at: <https://aliceo2group.github.io/analysis-framework/docs/tools/#running-with-o2physics-code-check>.
++ echo 'Found 1 errors and 0 warnings.'
Found 1 errors and 0 warnings.
++ [[ 1 -gt 0 ]]
++ cat /sw/BUILD/2bba9c137d4203939a43573e0f58059ebe644b05/O2Physics-code-check/errors.txt
PWGCF/MultiparticleCorrelations/Tasks/multiparticleCorrelationsMei.cxx:51:1: error: included header numeric is not used directly [misc-include-cleaner,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 1 -gt 0 ]]
++ exit 1
--

Full log here.