* Add Swift package registry support
* Fix Swift archive integrity handling
* Fix Swift registry pagination and archive HEAD requests
* Canonicalize Swift package identifiers
* Handle Swift registry cache identities
* Use stored PURLs for cache lookups
* Address review: upstream-hash refetch and cache PURL cleanup
- Re-fetch instead of 502 when a cached artifact's hash disagrees with
the upstream-declared checksum; log and discard the stale entry.
- Rename expectedHash to upstreamHash and document how the check
differs from checkCache's stream integrity verification.
- Drop the repository_url qualifier from swift cache PURLs so cache
entries survive an upstream.swift change, matching other ecosystems.
- Pass name to handleSourceArchiveHead instead of re-deriving it.
* Drop BulkCheckVulnerabilities coverage after #279 removed it
The rebase over #279 (dead-code cleanup) drops BulkCheckVulnerabilities;
remove the tests and helper that exercised the swift-identity-filtering
path through it, and the imports they pulled in.
