feat: Export isClientEnvironment function (#179)

* feat: extract client environment detection

* Create smooth-adults-tease.md

---------

Co-authored-by: Yongbeen Im <been.im@toss.im>
Co-authored-by: Yongbeen Im <meis1541@naver.com>

Author: Lee-WonJun

.changeset/smooth-adults-tease.md

@@ -0,0 +1,5 @@
+---
+"overlay-kit": patch
+---
+
+Export `isClientEnvironment` function for mocking

packages/src/utils/create-use-external-events.ts

@@ -2,12 +2,16 @@ import { useLayoutEffect } from 'react';
 import { createEmitter } from './emitter';
 
 const emitter = createEmitter();
-function useClientLayoutEffect(...args: Parameters<typeof useLayoutEffect>) {
+
+export function isClientEnvironment() {
   const isBrowser = typeof document !== 'undefined';
   const isReactNative = typeof navigator !== 'undefined' && navigator.product === 'ReactNative';
 
-  if (!isBrowser && !isReactNative) return;
+  return isBrowser || isReactNative;
+}
 
+function useClientLayoutEffect(...args: Parameters<typeof useLayoutEffect>) {
+  if (!isClientEnvironment()) return;
   useLayoutEffect(...args);
 }