fix: export AlsStore to assist with avoiding TS problems in consumers

lib/index.ts

@@ -1,2 +1,6 @@
 export { ServerTiming } from './server-timing.js';
-export { createTimingStore } from './create-store.js';
+
+// type AlsStore be exported because of
+// https://github.com/microsoft/TypeScript/issues/42873
+// consumers will need to import it to avoid that error
+export { type AlsStore, createTimingStore } from './create-store.js';