Add a benchmark for stages of event mixing

[saganatt]

• add a new benchmark to evaluate the current event mixing step-by-step
• some fixes to the old event mixing benchmark; unfortunately, it still crashes and I have no more time to investigate it
• remove a redundant line in ASoAHelpers benchmark

FYI @chefxxx @MykhailoShamrai

[github-actions]

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[ktf]

Why was this removed?

[saganatt]

I thought that this column is not used anywhere in the benchmark. But, indeed, maybe it influences the timing of iterating over the table.

[ktf]

Please, squash the commits which can be squashed together so that it's easier to review the changes.

[saganatt]

Please, squash the commits which can be squashed together so that it's easier to review the changes.

I cleaned the PR history.

[alibuild]

Error while checking build/O2/fullCI_slc9 for f3e0120 at 2025-10-08 05:54:

No log files found

Full log here.

[github-actions]

This PR did not have any update in the last 30 days. Is it still needed? Unless further action in will be closed in 5 days.