feat(Accordion): add close event

[hansemannn]

This PR adds the new "close" event for UAccordion, so both "open" and "close" are properly supported.

Example:

<template>
  <UContainer class="min-h-screen flex items-center">
    <UCard class="flex-1" :ui="{ background: 'bg-gray-50 dark:bg-gray-800/50', ring: 'ring-1 ring-gray-300 dark:ring-gray-700', divide: 'divide-y divide-gray-300 dark:divide-gray-700', header: { base: 'font-bold' } }">
      <p class="text-gray-500 dark:text-gray-400">
        <UAccordion :items="[{ label: 'Test me' }]" @open="onOpen" @close="onClose" />
      </p>
    </UCard>
  </UContainer>
</template>

<script setup>
function onOpen() {
  alert('open!')
}
function onClose() {
  alert('close!')
}
</script>

Fixes #2745

[benjamincanac]

Thanks! 😊