🍒 plugins/pressure: Use ulonglong for storing "total" time information

Using long unsigned int leads to issues with recent libdbus/Qt that cause ksystemstats to abort with an error about "ulong" not being a recognised type. To avoid that, use a type that we already use in other places.

(cherry picked from commit d0098f96)

Co-authored-by: Arjen Hiemstra ahiemstra@heimr.nl