feat: add Kademlia DHT high-level API and interop test node

[adust09]

Summary

High-level Kademlia DHT API (LibP2P.DHT.API) plus a three-role interop test binary (libp2p-kad-dht-node) that implements the libp2p/unified-testing kad-dht contract.

New modules

• LibP2P.DHT.API — provide, putValue, findProviders operations built on existing iterativeFindNode, dhtSendRequest, and record store primitives
• LibP2P.DHT.APISpec — 5 unit tests with mock DHT nodes (all pass)

Interop binary (interop/kad-dht-node/)

Three roles matching the unified-testing kad-dht test app contract:

• bootstrap — listens, publishes address to Redis, runs DHT server
• provider — dials bootstrap, calls provide + putValue, signals done via Redis
• querier — dials bootstrap, queries findProviders + iterativeGetValue, prints status pass/fail

Coordination uses Redis SET/GET (matching the Python reference), with {TEST_KEY}_bootstrap_addr and {TEST_KEY}_provider_done keys.

Docker / CI

• interop/kad-dht-node/Dockerfile — multi-stage build (GHC 9.10 to debian-slim, ~10MB)
• docker-compose.kad-dht.yml — self-test compose (redis + bootstrap + provider + querier)
• .github/workflows/interop.yml — new kad-dht-interop job
• interop/Makefile — kad-dht target

Housekeeping

• Transport interop relocated from interop/ to interop/transport/
• Ported transport interop to RPUSH/BLPOP Redis list contract (ref fix: use Redis RPUSH/BLPOP for interop listener coordination #263)

Test results

1134 examples, 0 failures

Ref: unified-testing PR #119 (nim precedent for this pattern)

Checklist

• Compiles (library + both executables)
• All 1134 tests pass (1129 existing + 5 new)
• API test suite covers provide, putValue, findProviders
• Dockerfile builds clean
• CI job defined for self-test (bootstrap -> provider -> querier)

[seetadev]

@adust09 : Thanks Shouki, this is a really great addition to libp2p-hs and to the broader libp2p ecosystem.

I reviewed the PR and the overall approach looks solid. In particular, it’s great to see the high-level Kademlia API built cleanly on top of the existing DHT primitives, with coverage for provide, putValue, and findProviders. The dedicated API tests are a strong addition as well.

The three-role interop test node is especially valuable. Following the unified-testing Kademlia contract with bootstrap, provider, and querier roles gives us a clear path toward exercising Haskell interoperability against the other libp2p implementations. I also appreciate the Redis coordination matching the established interop patterns, along with the dedicated Docker/CI setup.

The routing-table bootstrap fix and the transport interop housekeeping also make this feel like a well-rounded change rather than just adding the API surface. 1134 tests passing with 0 failures and all CI checks green is excellent.

From the libp2p maintainer side, LGTM! 👍 Thanks for the thorough implementation and for continuing to move libp2p-hs forward with proper interoperability and conformance testing. Happy to see this merged.