Maintainer updates for testing, gdbstub, semihosting, plugins - bump python in *BSD images via libvirt-ci - remove old unused Leon3 Avocado test - re-factor gdb command extension - add stoptrigger plugin to contrib - ensure plugin mem callbacks properly sized - reduce check-tcg noise of inline plugin test - fix register dumping in execlog plugin - restrict semihosting to TCG builds - fix regex in MTE test