[markverick]

Related to #145 and #242.

Expose DV2 routing and forwarding information through signed datasets and a combined status page.

• Publish signed, versioned, segmented routing snapshots at /<router-name>/32=DV/32=STATUS.
• Include reachable routers, selected next hops, routing costs, PSD entry counts, and prefix multicast flags and validity periods.
• Maintain PET egress mappings for remote dataset retrieval.
• Replace the BIFT management dataset’s JSON payload with TLV and update its consumers.
• Add XML/JSON status reports and an HTTP server exposing HTML, /status.xml, and /status.json.
• Include forwarder statistics, faces, FIB/RIB, PET mappings, BIER/BIFT state, content-store statistics, and strategies.
• Validate routing datasets using explicit trust anchors and an optional custom schema, without falling back to unvalidated data.
• Correct the outgoing face-byte counter used by the reports.

Snapshots are generated outside the packet-processing loop, cached for one second, and retain a bounded version history. The existing /localhost/dv/status endpoint remains available.

Prefix details cover reachable routers rather than the complete PSD. The BIFT wire-format change requires updating the forwarder and consumers together.