Replace sleep with wait-for-tcp script in run-tests.sh and CI workflow to improve reliability of smoke tests. Update TESTING.md to include prerequisites for the new script.

scripts/ci/wait-for-tcp.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+set -e
+host=${1:-127.0.0.1}
+port=${2:-2222}
+max_attempts=${3:-30}
+for _ in $(seq 1 "$max_attempts"); do
+  if nc -z -w 1 "$host" "$port" 2>/dev/null; then
+    exit 0
+  fi
+  sleep 1
+done
+echo "timeout waiting for $host:$port" >&2
+exit 1