[FR] “Sparse” peerings

Nobody has claimed this yet.

### What

Peerings with “sparse” status, an explicit opt in on both sides go allow a connection more low-throughput, high-latency, more unreliable, or with less duty cycles than the current pinecone peerings require.

### Why

Primarily, iot devices, to allow for power savings, yet stay connected to the network at times, allowing peers at the other side of the sparse connection to queue up packets and send them through whenever the underlying transport allows.

Secondly, resiliency in unreliable conditions, where a peer wants to accept high-latency costs, at the benefit of not becoming disconnected from the network at large. (Think remote outposts in unfavourable weather conditions resulting in unreliable uplinks, or network operators in hostile environments requiring prolonged connectivity over intermittent outages)

No files, tests, or entry points are named. Start by tracing how Pinecone represents peerings and connection state, then determine the protocol and queueing behavior required for an explicit sparse opt-in on both sides. Done means sparse peers remain connected through intermittent, low-throughput links while queued packets can be sent when transport permits.

Written by the indexing model from the issue text.