refactor: normalize export pattern for nodeRuntimeImportCache

Use direct export declaration instead of separate export statement
to match the pattern used by all other exports in the file.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: ScriptedAlchemy

packages/node/src/runtimePlugin.ts

@@ -39,10 +39,7 @@ type WebpackRequire = {
 declare const __webpack_require__: WebpackRequire;
 declare const __non_webpack_require__: (id: string) => any;
 
-const nodeRuntimeImportCache = new Map<string, Promise<any>>();
-
-// Export cache for testing
-export { nodeRuntimeImportCache };
+export const nodeRuntimeImportCache = new Map<string, Promise<any>>();
 
 export function importNodeModule<T>(name: string): Promise<T> {
   if (!name) {