regression kad-dht: v2.2.0 pin + open publish endpoint before bootstrap

Bump nim-libp2p to release/v2.2.0 (d721f9c). Move startHttpServer to right
after switch.start() so a stalled kad bootstrap can't leave a node without its
:8645 publish port (verified at 1000 nodes: injection holds even when only
~a third complete bootstrap).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nim-test-node/regression/main.nim

@@ -274,6 +274,11 @@ proc main {.async.} =
   switch.mount(pingProtocol)
   await switch.start()
 
+  # Open the publish endpoint up-front, before the kad-dht bootstrap below, so a
+  # stalled bootstrap can't keep a node from ever opening :8645.
+  info "Starting listening endpoint for publish controller"
+  discard gossipSub.startHttpServer(myId)
+
   # Metrics
   info "Starting metrics server"
   let metricsServer = startMetricsServer(parseIpAddress("0.0.0.0"), prometheusPort)
@@ -310,9 +315,6 @@ proc main {.async.} =
   # Periodic mesh-only pings
   asyncSpawn pingMeshLoop(switch, pingProtocol, gossipSub, "test")
 
-  info "Starting listening endpoint for publish controller"
-  discard gossipSub.startHttpServer(myId)
-
   await sleepAsync(2.days)
 
 waitFor(main())

nim-test-node/regression/test_node.nimble

@@ -11,5 +11,5 @@ skipDirs      = @[]
 
 requires "nim >= 2.2.0",
           "nimcrypto 0.6.4",
-          "https://github.com/vacp2p/nim-libp2p#c470b1146fa2ef23ab88c5a0940923cf7645e9c5", # 2.1.0
+          "https://github.com/vacp2p/nim-libp2p#d721f9cb13c36b844957556ac04fecade371b059", # release/v2.2.0
           "ggplotnim"