Currently, artifact references in podman/containers tools don't have proper validation and enforcement of naming rules, leading to inconsistent behavior compared to images. We need to create a new ArtifactReference type in containers/common that enforces the following rules:

• No shortname resolution (unlike images, artifacts should require fully-qualified names)
• Proper validation of artifact references at construction time
• Support for digest-based references
• Consistent behavior across all artifact operations

This addresses issues identified in https://github.com/containers/container-libs/issues/406 where:

• Shortname resolution causes confusion and credential passing issues (especially in CRI-O/Kubernetes)
• Missing digest support for artifacts pulled by tag
• Inconsistent handling compared to image references

Implementation approach:
Create a new ArtifactReference type containing something like a named.Digested reference, with a New constructor that validates all rules and returns errors on invalid references. This will be a type change in the containers/common API.

Cloned from RUN-3630 for container-libs code review.