* Accept Swift source repository PURLs in the denylist and retention rules
Closes#613. pkg:swift/github.com/apple/swift-nio, as SBOM tools and GHSA
write Swift packages, is resolved to its registry identity through the
upstream's /identifiers:
- Denylist entries are resolved at startup, and the proxy refuses to start
when one can't be, since a skipped entry would let the version through.
- Retention keys are accepted at validation and kept pending. The
retention loop resolves them before each sweep, and Swift isn't swept
while any is pending, so a rule that keeps a package is never skipped.
The mirror's source URL helper moves to the handler as SwiftSourceURL.
* Resolve Swift source denylist entries in proxy mirror too
serve resolved source-form Swift denylist entries through the upstream,
but proxy mirror built its denylist directly, so such an entry never
matched a mirror download. Both now use server.ConfigureDenylist, and
neither runs when an entry can't be resolved.
* Apply Swift source policies to every listed identity
A Swift registry may list several identities for one source repository,
but a denylist entry or retention rule naming the repository only
covered the first. Denying pkg:swift/github.com/acme/widget@1.0.0 let
acme.widget through when the registry listed other.widget first, and a
never-evict rule cleared the cached apple.swift-nio archive when
other.swift-nio came first.
Both now cover every identity the registry lists. A retention rule that
conflicts with another rule for any of them stays pending, with none
applied. Mirroring a source PURL still downloads the first identity.
