Optimize events on handler

By storing the targets only once per base node we spare some
unneccessary dom queries.

app/javascript/alchemy_admin/utils/events.js

@@ -1,7 +1,8 @@
 export function on(eventName, baseSelector, targetSelector, callback) {
   document.querySelectorAll(baseSelector).forEach((baseNode) => {
+    const targets = Array.from(baseNode.querySelectorAll(targetSelector))
+
     baseNode.addEventListener(eventName, (evt) => {
-      const targets = Array.from(baseNode.querySelectorAll(targetSelector))
       let currentNode = evt.target
 
       while (currentNode !== baseNode) {