maven: parse all version-bearing references

[andrew]

Yul checks prospective pom.xml edits and needs to inspect every directly declared coordinate whose version can change. The Maven parser currently returns effective project dependencies from ep.Dependencies, which omits several declarations that Yul checks today:

• parent
• dependencyManagement
• build plugins
• plugin dependencies
• pluginManagement
• build extensions
• each of those declarations inside profiles

Could the Maven parser expose these version-bearing references while preserving enough information to distinguish their kind and profile? Consumers comparing before and after manifest content need the declarations themselves rather than only the effective dependency set.

This affects manifests v0.6.1. A characterization suite for the intended consumer behavior is in chains-project/yul#1.

[andrew]

The supporting POM change is merged and released, and the manifests API is ready for review:

• git-pkgs/pom#18 is merged and available in v0.1.7. It exposes plugin dependencies and the other POM structures needed by the manifest parser.
• git-pkgs/manifests#67 is ready for review. It adds format-neutral Declaration values and populates them for Maven parents, dependencies, plugins, plugin dependencies, extensions, management blocks, and profile-scoped declarations.
• chains-project/yul#12 is a draft consumer. It removes the custom Yul POM parser and Maven Central client, then uses manifest declarations with the shared pin comparison and enrichment resolver. The characterization coverage still includes every Maven declaration type listed in this issue.

The remaining work is to merge manifests#67, tag a manifests release, then replace the pseudo-version in the Yul draft and mark it ready for review. PR #67 covers the parser behavior requested here; the release is needed for Yul to consume it without pinning a commit.