Fix account registration exports

Destructuring the implemenation and exporting its functions does not
work because it only happens when the module evaluates. Instead, we can
export wrapped versions of the implementation functions.

src/auth/index.ts

@@ -1,7 +1,16 @@
 import { impl } from "./implementation.js"
 
-const {  isUsernameAvailable, isUsernameValid, register } = impl
+export const register = async (options: { username: string; email: string }): Promise<{ success: boolean }> => {
+  return impl.register(options)
+}
+
+export const isUsernameValid = async (username: string): Promise<boolean> => {
+  return impl.isUsernameValid(username)
+}
+
+export const isUsernameAvailable = async (username: string): Promise<boolean> => {
+  return impl.isUsernameAvailable(username)
+}
 
-export { isUsernameAvailable, isUsernameValid, register }
 export { AccountLinkingRequestor, createConsumer as createRequestor } from "./linking/consumer.js"
 export { AccountLinkingProvider, createProducer as createProvider } from "./linking/producer.js"