Link the verify install plugin to the artifact plugin

[vaibhavdaren]

Problem Statement

As a developer working on the verify-installation plugin (PR #4660), I need two follow-up improvements to make the plugin easier to test in isolation and more useful in real-world workflows:

1. Test structure is unnecessarily split. The current tests use separate data-centos/data-fedora directories.

2. The plugin has no integration with prepare/artifact. When a user specifies packages via prepare/artifact for a provider whose artifacts are declared in artifacts.yaml (e.g. Copr, Brew, koji), the verify-installation plugin currently has no way to automatically know which repository those packages are expected to come from. The user must manually duplicate this information. Instead, the plugin should be able to derive the expected repo from the artifact provider configuration already present in the plan.

Out of Scope

• Adding new providers to artifacts.yaml (that is a separate concern).
• Support for package managers other than dnf4/dnf5 (already tracked separately).