Pack TSOS so as to be back at size 48 rather than 56 (see ATLASSIM-6072)

The issue is discussed at [https://its.cern.ch/jira/browse/ATLASSIM-6072]

The gist of what happened is here [https://godbolt.org/z/vfaxozhqK]

by splitting we ended up with >15% the size in memory. This then had some visible effects .

ping @ssnyder