Primitive Docker tag validation helpers for `RustUse`.
`use-docker-tag` validates Docker-shaped tag text and exposes small helpers for
`latest`, semantic-looking tags, and platform-looking suffixes.
```rust
use use_docker_tag::DockerTag;
let tag: DockerTag = "1.2.3-alpine".parse()?;
assert!(tag.is_semver_like());
assert!(tag.has_platform_suffix());
assert_eq!(DockerTag::latest().as_str(), "latest");
```