use avif sponsor images

Author: yyx990803

.vitepress/theme/components/SponsorsGroup.vue

@@ -62,7 +62,14 @@ onMounted(async () => {
         target="_blank"
         rel="sponsored noopener"
       >
-        <img :src="`${base}/images/${img}`" :alt="name" />
+        <picture v-if="img.endsWith('png')">
+          <source
+            type="image/avif"
+            :srcset="`${base}/images/${img.replace(/\.png$/, '.avif')}`"
+          />
+          <img :src="`${base}/images/${img}`" :alt="name" />
+        </picture>
+        <img v-else :src="`${base}/images/${img}`" :alt="name" />
       </a>
     </template>
     <a