Fix pause to cancel probe goroutine; add Robot Framework integration tests

Pause semantics
- PauseBackend now cancels the probe goroutine so no HTTP/TCP/ICMP
  traffic is sent while the backend is paused. Previously the goroutine
  kept running and results were silently discarded.
- ResumeBackend launches a fresh probe goroutine on the existing worker,
  preserving transition history. The backend re-enters unknown state.

Integration tests (tests/01-maglevd/)
- Containerlab topology with 3 nginx:alpine backends on a dedicated
  management network (172.20.30.0/24) with static IPs.
- maglevd config with 200ms HTTP health-check interval for fast test
  convergence (rise=2, fall=2).
- 8 test cases: deploy lab, start maglevd, all backends reach up,
  nginx logs confirm probes arriving, pause stops probes (probe count
  stable), resume restarts probes, disable stops probes, enable
  restarts probes.

VPP dataplane test (tests/02-vpp-lb/)
- Rewrite 01-e2e-lab.robot to match the actual single-VPP topology:
  test client-to-server ping through VPP bridge domains and verify
  nginx is serving on all app servers. The previous version referenced
  a non-existent topology file and tested OSPF/BFD between two VPP
  nodes that don't exist in this lab.

Build infrastructure
- Add 'make robot-test' target with TEST= for suite selection.
- Add tests/.venv target for Robot Framework virtualenv.
- Make IMAGE optional in rf-run.sh.
- Add .gitignore entries for test output, venv, logs, and clab state.

tests/02-vpp-lb/e2e-lab/config/as1/rc.local

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+MYIP=$(ip addr show dev eth1 | awk '/inet .*scope/ { print $2}' | cut -f1 -d/)
+
+ip tunnel add maglev0 mode gre local $MYIP
+ip link set maglev0 up mtu 1500
+ip addr add 10.82.98.255/32 dev maglev0
+
+echo "This is $(hostname -f)" >> /usr/share/nginx/html/index.html

tests/02-vpp-lb/e2e-lab/config/as2/rc.local

@@ -0,0 +1 @@
+../as1/rc.local

tests/02-vpp-lb/e2e-lab/config/as3/rc.local

@@ -0,0 +1 @@
+../as1/rc.local

tests/02-vpp-lb/e2e-lab/config/vpp1/manual-post.vpp

@@ -0,0 +1,12 @@
+comment { You can add commands here that will execute after vppcfg.vpp }
+lb conf ip4-src-address 10.82.98.0 ip6-src-address 2001:db8:8298:: buckets 524288
+lb vip 10.82.98.255/32 protocol tcp port 80 
+lb as 10.82.98.255/32 protocol tcp port 80 10.82.98.82
+lb as 10.82.98.255/32 protocol tcp port 80 10.82.98.83
+lb as 10.82.98.255/32 protocol tcp port 80 10.82.98.84
+
+lb vip 10.82.98.255/32 protocol tcp port 443 src_ip_sticky
+lb as 10.82.98.255/32 protocol tcp port 443 10.82.98.82
+lb as 10.82.98.255/32 protocol tcp port 443 10.82.98.83
+lb as 10.82.98.255/32 protocol tcp port 443 10.82.98.84
+

tests/02-vpp-lb/e2e-lab/config/vpp1/vppcfg.yaml

@@ -0,0 +1,45 @@
+loopbacks:
+  loop0:
+    description: "Core: vpp1"
+    lcp: loop0
+    addresses: [10.82.98.0/32, 2001:db8:8298::/128]
+  loop1:
+    description: "Core: Maglev VIP"
+    lcp: maglev0
+  loop2:
+    description: "BVI: clients"
+    mtu: 1500
+    lcp: bvi101
+    addresses: [10.82.98.65/28, 2001:db8:8298:101::1/64]
+  loop3:
+    description: "BVI: application servers"
+    mtu: 2026
+    lcp: bvi102
+    addresses: [10.82.98.81/28, 2001:db8:8298:102::1/64]
+bridgedomains:
+  bd101:
+    description: "Clients"
+    mtu: 1500
+    bvi: loop2
+    interfaces: [ eth1, eth2 ]
+  bd102:
+    description: "Application Servers"
+    mtu: 2026
+    bvi: loop3
+    interfaces: [ eth3, eth4, eth5 ]
+interfaces:
+  eth1:
+    description: "To cl1:eth1"
+    mtu: 1500
+  eth2:
+    description: "To cl2:eth1"
+    mtu: 1500
+  eth3:
+    description: "To as1:eth1"
+    mtu: 2026
+  eth4:
+    description: "To as2:eth1"
+    mtu: 2026
+  eth5:
+    description: "To as3:eth1"
+    mtu: 2026

tests/02-vpp-lb/e2e-lab/maglev.clab.yml

@@ -0,0 +1,64 @@
+name: e2e-maglev
+
+topology:
+  kinds:
+    fdio_vpp:
+      image: git.ipng.ch/ipng/vpp-containerlab:latest
+      startup-config: config/__clabNodeName__/vppcfg.yaml
+      binds:
+        - config/__clabNodeName__/manual-post.vpp:/config/vpp/config/manual-post.vpp:rw
+    linux:
+      image: ghcr.io/srl-labs/network-multitool:latest
+      binds:
+        - config/__clabNodeName__/rc.local:/config/rc.local:rw
+
+  nodes:
+    vpp1:
+      kind: fdio_vpp
+    cl1:
+      kind: linux
+      exec:
+        - ip addr add 10.82.98.66/28 dev eth1
+        - ip route add 10.82.98.0/24 via 10.82.98.65
+        - ip addr add 2001:db8:8298:101::2/64 dev eth1
+        - ip route add 2001:db8:8298::/48 via 2001:db8:8298:101::1
+        - sh /config/rc.local
+    cl2:
+      kind: linux
+      exec:
+        - ip addr add 10.82.98.67/28 dev eth1
+        - ip route add 10.82.98.0/24 via 10.82.98.65
+        - ip addr add 2001:db8:8298:101::3/64 dev eth1
+        - ip route add 2001:db8:8298::/48 via 2001:db8:8298:101::1
+        - sh /config/rc.local
+    as1:
+      kind: linux
+      exec:
+        - ip addr add 10.82.98.82/28 dev eth1
+        - ip route add 10.82.98.0/24 via 10.82.98.81
+        - ip addr add 2001:db8:8298:102::2/64 dev eth1
+        - ip route add 2001:db8:8298::/48 via 2001:db8:8298:102::1
+        - sh /config/rc.local
+    as2:
+      kind: linux
+      exec:
+        - ip addr add 10.82.98.83/28 dev eth1
+        - ip route add 10.82.98.0/24 via 10.82.98.81
+        - ip addr add 2001:db8:8298:102::3/64 dev eth1
+        - ip route add 2001:db8:8298::/48 via 2001:db8:8298:102::1
+        - sh /config/rc.local
+    as3:
+      kind: linux
+      exec:
+        - ip addr add 10.82.98.84/28 dev eth1
+        - ip route add 10.82.98.0/24 via 10.82.98.81
+        - ip addr add 2001:db8:8298:102::4/64 dev eth1
+        - ip route add 2001:db8:8298::/48 via 2001:db8:8298:102::1
+        - sh /config/rc.local
+
+  links:
+    - endpoints: ["vpp1:eth1", "cl1:eth1"]
+    - endpoints: ["vpp1:eth2", "cl2:eth1"]
+    - endpoints: ["vpp1:eth3", "as1:eth1"]
+    - endpoints: ["vpp1:eth4", "as2:eth1"]
+    - endpoints: ["vpp1:eth5", "as3:eth1"]