Fix CI integration test failures

Two breakages in the integration test steps:

1. `pip install -U pymodbus` pulls pymodbus 3.x, which removed
   `pymodbus.server.sync` and `ModbusBinaryFramer`. server.py crashes
   on import, leaving the modbus client step to time out against a
   port nothing is listening on. Pin to pymodbus<3 so the existing
   server.py still imports, and pin Python to 3.11 since pymodbus
   2.5.3 has not been validated against newer interpreters.

2. Servers are backgrounded with `&` and the next step runs the
   client immediately, racing the listen socket. Add explicit
   wait-for-port steps using bash's /dev/tcp before each client
   runs, and capture server output to /tmp logs so a failure surfaces
   diagnostics instead of just timing out.

Also `nohup` the backgrounded servers and redirect their output so
they survive the step boundary cleanly without printing into the
runner log mid-step.

Author: claude

.github/workflows/ci.yml

@@ -30,24 +30,45 @@ jobs:
         ./setup_posix.sh
         make
         sudo setcap cap_net_raw+ep ./src/ports/POSIX/OpENer
-        ./src/ports/POSIX/OpENer lo &
+        nohup ./src/ports/POSIX/OpENer lo > /tmp/opener.log 2>&1 &
+
+    - name: Wait for OpENer to listen on 44818
+      run: |
+        for i in {1..30}; do
+          if (exec 3<>/dev/tcp/127.0.0.1/44818) 2>/dev/null; then
+            exec 3<&- 3>&-
+            exit 0
+          fi
+          sleep 1
+        done
+        echo "OpENer did not start listening on 44818" >&2
+        cat /tmp/opener.log >&2 || true
+        exit 1
 
     - working-directory: node-drivers
       run: node test/integration/eip.js
 
     - uses: actions/setup-python@v5
       with:
-        python-version: '3.x'
-    
+        python-version: '3.11'
+
     - working-directory: node-drivers
       run: |
-        pip install -U pymodbus
-        python ./test/integration/modbus/server.py &
+        pip install 'pymodbus<3'
+        nohup python -u ./test/integration/modbus/server.py > /tmp/modbus-server.log 2>&1 &
+
+    - name: Wait for modbus server to listen on 5020
+      run: |
+        for i in {1..30}; do
+          if (exec 3<>/dev/tcp/127.0.0.1/5020) 2>/dev/null; then
+            exec 3<&- 3>&-
+            exit 0
+          fi
+          sleep 1
+        done
+        echo "Modbus server did not start listening on 5020" >&2
+        cat /tmp/modbus-server.log >&2 || true
+        exit 1
 
     - working-directory: node-drivers
       run: node test/integration/modbus/client.js
-      
-
-
-
-