Model build.zig.zon package dependencies for replacement parity

[godofecht]

Problem

Azazel records package intent today, but replacement parity requires richer build.zig.zon modeling.

Needed

• Parse/record dependency names, URLs, hashes, paths, lazy flags, and package modules.
• Preserve dependency aliases used by module imports.
• Distinguish dependency-fetch failures from package-format failures.
• Support dependency cache roots in reproducible runner output.

Corpus drivers

• ZLS uses multiple package dependencies and generated version data.
• MicroZig hits dependency zip handling.
• Capy exposes transitive package-format drift.
• zig-gamedev has a large dependency graph that now builds on 0.15.2.

Done when

• Corpus manifests include enough dependency metadata to explain missing/failing deps without reading upstream build scripts manually.
• --build classifications remain stable across fresh clone roots.
• A first Azazel target slice can import a build.zig.zon dependency module.