Testing, gdbstub and plugin updates: - fix some test/tcg license headers to GPLv2+ - bump up check-tcg timeout to 120s - avoid re-building VM images too often - update OpenBSD to 7.4 - use GDBFeature to build gdbstub XML - unify plugin vcpu count under qemu_plugin_num_vcpus - avoid spurious idle/resume callbacks on new vCPUs - ensure nios2-linux-user processes async work - call vcpu_init plugin callback through async work - define plugin helpers when registers being read - add plugin API for reading register values - add support for register tracking to execlog - update plugin docs with assumptions - mention plugins can trigger tb_flush in mttcg design doc