[FEATURE] Provide function that maps agent key to peer ID using network stat and dump

[zippy]

dumpNetworkMetrics and dumpNetworkStats are today the only source of network observability, but they are built as human diagnostic dumps, not as an API:

1. Wrong key space. Results are keyed by kitsune SpaceId and transport pub keys / peer URLs, not DnaHash and AgentPubKey. A client must reverse-engineer the correlation itself.

2. Too expensive to poll. Inside the conductor each call runs a serial per-DNA loop over the app's cells (conductor.rs:2509-2567 as of 0.7), and nothing coordinates or throttles polling across clients.

3. Untyped payloads. Portions of the dump arrive as nested JSON strings that clients must double-parse

Proposal:

• Return metrics keyed by DnaHash/CellId and AgentPubKey, with the transport-level identifiers included alongside rather than instead. The conductor holds the space_id ↔ DNA and agent↔transport mappings; clients should never re-derive them. (This becomes mandatory under the access4 design, where space_id is one-way derived from the DNA hash and clients cannot reverse it.)
• Make the common read cheap: cache/snapshot metrics conductor-side so a per-cell query doesn't walk every cell, or better, offer a subscription (emit on change / at a fixed cadence) so clients stop polling entirely.
• Replace stringly-typed payloads with structured types in holochain_conductor_api (which also gets them into the TS bindings via ts_rs).

Related: holochain/holochain#4664 (dump_* should return structs, not serialized strings — this issue is the network-specific superset), holochain/holochain#3315 (network info wish list), holochain/holochain#5134 (expose access metrics — will land in this same API surface and should follow the same conventions), kitsune2#266. Complements the per-cell sync-status API proposal: that one covers "is this cell healthy/synced", this one covers the underlying metrics plumbing being correct and affordable.

[jost-s]

Leave it up to apps to poll, but with a new convenience function that queries network stats and metrics and matches the agent key to the transport's peer ID.