MILAN — The Hungarian government and its state-owned holding N7 have signed three joint ventures in December alone, part of a large-scale spending spree for new weapons and production plants. The deals, involving major foreign defense manufacturers, come amid a reported shortage of personnel to operate and build the equipment. Over the past few years, the European country has embarked on a journey to modernize and bolster its defense-industrial base, having neglected it for well over a decade.