fix(ci): harden Molecule download and cleanup

- Retry transient k3s release downloads with bounded backoff.\n- Bound failure diagnostics and validate guest release connectivity.\n- Discover repository-owned Molecule state under the actual project root.

.github/workflows/test.yml

@@ -9,12 +9,12 @@ jobs:
     strategy:
       matrix:
         scenario:
-          - default
-          # - ipv6
           - single_node
           - calico
           - cilium
           - kube-vip
+          - default
+          # - ipv6
       fail-fast: false
       max-parallel: 1
     env: