CVE-2026-73974: linuxfabrik-lib: Arbitrary root file read via live --test argument (lib.lftest) across sudoers-whitelisted plugins (LPE)

Every Linuxfabrik check plugin that supports the shared --test argument (routed through lib.lftest.test()) will, when --test is supplied, treat the first CSV element as a filesystem path and read its full contents as the plugin’s simulated STDOUT — running as root when the plugin is invoked through the shipped nagios/icinga sudoers allowlist. --test is a live production argument (centrally mapped to argparse.SUPPRESS, so it is hidden from --help but still accepted on the command line), not a build-time-only gate. This yields an arbitrary root file-read primitive (full disclosure on deb-updates; filtered disclosure / existence-and-readability oracle on ~22 other whitelisted plugins), i.e. local privilege escalation from the nagios account to root.