feat(ci): optimize Molecule VM creation

- reuse validated runner-owned Vagrant linked-clone masters\n- create the default guests in bounded two-machine batches\n- capture create timing and runner utilization diagnostics

.github/scripts/vagrant-up-timed.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+
+set -Eeuo pipefail
+
+if (($# < 2)); then
+  printf 'Usage: vagrant-up-timed.sh WORKDIR MACHINE [MACHINE ...]\n' >&2
+  exit 2
+fi
+
+workdir="$1"
+shift
+timing_log="${K3S_CI_CREATE_TIMING_LOG:-${RUNNER_TEMP:-/tmp}/k3s-ci-create-timing.log}"
+mkdir -p -- "${timing_log%/*}"
+
+printf '%s batch-start machines=%s\n' "$(date --iso-8601=ns)" "$*" | tee -a "$timing_log"
+set +e
+VAGRANT_CWD="$workdir" vagrant up "$@" --provider virtualbox --no-provision 2>&1 |
+  while IFS= read -r line; do
+    printf '%s %s\n' "$(date --iso-8601=ns)" "$line"
+  done | tee -a "$timing_log"
+rc=${PIPESTATUS[0]}
+set -e
+printf '%s batch-end rc=%d machines=%s\n' "$(date --iso-8601=ns)" "$rc" "$*" | tee -a "$timing_log"
+exit "$rc"