Fix linting issues - use longform method syntax for string literal keys

Co-authored-by: mattcosta7 <8616962+mattcosta7@users.noreply.github.com>

Author: Copilot

lib/rules/prefer-observers.js

@@ -58,7 +58,7 @@ export default {
       },
 
       // Check addEventListener calls
-      ['CallExpression[callee.property.name="addEventListener"]'](node) {
+      ['CallExpression[callee.property.name="addEventListener"]']: function (node) {
         const [name] = node.arguments
         if (name.type !== 'Literal') return
         if (!(name.value in observerMap)) return
@@ -76,7 +76,7 @@ export default {
       },
 
       // Check ResizeObserver.observe() calls
-      ['CallExpression[callee.property.name="observe"]'](node) {
+      ['CallExpression[callee.property.name="observe"]']: function (node) {
         // Check if this is a ResizeObserver instance
         const callee = node.callee
         if (!callee.object) return