Krikri::PluginHelpers::RpmPackage

Shared implementation for the RPM-family package-manager plugins (plugins/yum.cr, plugins/dnf.cr): every method here was a byte-identical (modulo the binary name / comment verbosity) copy in both files, and the copies had already drifted once (yum's install path gained the classify/batch refactor dnf never got). Included as INSTANCE methods into both plugin classes, so they dispatch through the includer's own remote_exec/@params/true? - the only per-plugin input is #pkg_manager_binary, which each plugin defines as a one-liner.

NOTE: the two plugins' execute and install/absent handling are still per-plugin (yum's install path has the newer classify/batch shape; dnf's is the older monolith) - unify those only as part of a deliberate behavioral alignment, not by wholesale deletion.