fix(molecule): stabilize default scenario networking

- serialize five-node Vagrant creation to avoid VirtualBox host-only races
- refresh and verify the primary neighbor mapping before convergence
- include interface MAC details in failure diagnostics

roles/k3s_server/tasks/fetch_k3s_init_logs.yml

@@ -30,6 +30,14 @@
   no_log: true
   register: k3s_ip_address_state
 
+- name: Fetch IP link state
+  ansible.builtin.command:
+    cmd: ip -br link
+  changed_when: false
+  failed_when: false
+  no_log: true
+  register: k3s_ip_link_state
+
 - name: Fetch IP route state
   ansible.builtin.command:
     cmd: ip route show
@@ -136,6 +144,9 @@
       === ip -br address ===
       {{ k3s_ip_address_state.stdout }}
 
+      === ip -br link ===
+      {{ k3s_ip_link_state.stdout }}
+
       === ip route show ===
       {{ k3s_ip_route_state.stdout }}