Add caching of privileges (or entire result) for get auth function

[Leslie Krause]

No description provided.

[PICCORO McKAY Lenz]

i noted that this mod always assumed a migration so right admin handle is not fixed https://codeberg.org/minenux/minetest-mod-auth_rx/commit/15143fd58fae3de7269d35521c1ccf020b84e829