Small improvements to cbm::algo::tof::Clusterizer.

Minor improvments and fixes.

added Online label

requested review from @d.smith

assigned to @d.smith

enabled an automatic merge when the pipeline for b9a9f2a0 succeeds

@fweig FYI: I tried introducing a "QA mode" here, such that the digi indices are only stored if a flag is set. The gains this produced were negligible, so I dropped it again.

Dear @n.herrmann, @i.deppner,

you have been identified as code owner of at least one file which was changed with this merge request.

Please check the changes and approve them or request changes.

added CodeOwners label

merged