feat: Add initialAuth to AuthkitProvider

[danielr18]

Fixes #295

AuthKitProvider was always fetching auth data on mount. Added an optional initialAuth prop so you can pass the data directly from your server component and skip the unnecessary round trip.

Example:

export default async function RootLayout({ children }) {
  const auth = await withAuth();
  const { accessToken, ...initialAuth } = auth;

  return (
    <AuthKitProvider initialAuth={initialAuth}>{children}</AuthKitProvider>
  );
}

Not sure if this is the best approach, but there should be a way to avoid the server action call on every initial mount if preferred.