Features
- net/transport/iroh: iroh transport with relay fallback (#768)
- keyvalue: prefix deletion watermark (#759)
- net: quic degradation fallback, demoting peers to yamux-first (#774, #775)
- net: advisory peer connection observer (#773)

Fixes
- ocache: refuse to close an entry that is still loading (#769)
- app: close only the components Init reached (#770)
- headsync: subscribe to head storage from Init, fixing a data race on the
  observer slice; fill the diff before draining buffered updates (#772, #776)
- net/pool: evict an outgoing peer that closed before the cache published it (#777)