Fix: timeclock: allow overlapping sessions with same account name

[brymut]

This PR fixes a regression that broke existing timeclock files containing overlapping sessions with the same account name. The issue was in pairClockEntries function which added a validation that prevented clock-in entries for accounts that already had active sessions.

However, the existing findInForOut logic already had handling for multiple sessions with the same account name using partition to correctly pair clock-ins with clock-outs.

Closes #2417

Added test

[brymut]

Hi @simonmichael, made an attempt at #2417 here.
Edit: Apologies, may have found some issues with my approach. Will Draft this PR until I figure it out.

[simonmichael]

For next release at least, the regression has been resolved by documenting the limitation, so I'm closing this. We can revisit, see #2417 for discussion.