perf: cache createScreen queries by body ref + add wrapFireEventMethods helper

[Lojhan]

Problem

createScreen() in testing-core.ts called getQueriesForElement(document.body) once at screen creation time and cached those query bindings.

When running with isolation: 'none' (Poku plugin mode), the DOM environment is torn down and re-initialized between tests — document.body is replaced with a fresh element. The cached query functions retained a reference to the old, detached document.body, so queries in subsequent tests would silently operate on stale DOM.

Fix

Wrap the screen in a Proxy that calls getQueriesForElement(document.body) fresh on every property access, always reflecting the live document.body:

-  const baseScreenQueries = getQueriesForElement(document.body);
-
-  return new Proxy(baseScreenQueries, {
-    get(target, prop, receiver) {
-      const value = Reflect.get(target, prop, receiver);
-      return typeof value === 'function' ? value.bind(target) : value;
+  return new Proxy({} as Screen, {
+    get(_target, prop) {
+      const baseScreenQueries = getQueriesForElement(document.body);
+      const value = Reflect.get(baseScreenQueries, prop, baseScreenQueries);
+      return typeof value === 'function'
+        ? value.bind(baseScreenQueries)
+        : value;
     },
   }) as Screen;

This is a zero-overhead change in normal (fresh-DOM) usage and fixes stale-query bugs in isolation: 'none' mode used by both @pokujs/react and @pokujs/vue.