fix(generic-oauth): async mapProfileToUser breaks

After debugging for an unacceptable amount of time, I found out that our generic oauth plugin with `mapProfileToUser` breaks when users apply `async` to their function despite our function signature supporting this. It breaks because we didn't use `await`...

packages/better-auth/src/plugins/generic-oauth/index.ts

@@ -329,7 +329,7 @@ export const genericOAuth = (options: GenericOAuthOptions) => {
 								emailVerified: userInfo?.emailVerified,
 								image: userInfo?.image,
 								name: userInfo?.name,
-								...c.mapProfileToUser?.(userInfo),
+								...(await c.mapProfileToUser?.(userInfo)),
 							},
 							data: userInfo,
 						};