Source type is now inferred from the primary key:
github_repo = owner/repo (was source=github + owner + repo)
git_url = https://... (was source=gittag + url)
gitea_repo = owner/repo (was source=gitea + owner + repo)
hashicorp_product = name (was source=hashicorp + product)
One-off dist sources (nodedist, zigdist, etc.) keep the explicit
source= key since they're already one-liners.
Parser still accepts the old format via the default fallback branch.
Declarative key=value config files that specify the release source
(github or nodedist), owner/repo, and optional tag_prefix for
monorepo packages. These replace the per-package releases.js logic
for the Go rewrite.
