That's all server-side code, which is the normal thing for luanti mods and games.
Client-side modding is currently a bit crude and limited, and requires a bit of funky manual installation, but allows you to read and alter some things on the client that aren't available to the server code. Client-side modding (CSM) was added a bit prematurely and is still in kind of a proof-of-concept stage; it was intended to be a step towards server-sent client-side modding (SSCSM) which will allow games to customize the behavior of the client.
For Exile we have an optional CSM for handling special keypresses, since reading key sequences can be difficult with lag over multiplayer, but 99.9% of our code is just the regular server-side code.
I'd like to take a moment to thank Lemmy for logging me out so I never saw the notice that you'd replied. :D
Yes, Luanti sends textures and sounds to the clients, though they are cached so it's only the first time you connect to a server.
Those games have an api of their own, though I don't know about "easier," and I'm not familiar with the specifics there as I don't particularly care for Minecraft. Odds are you'll need to override the beds behavior somehow, but I doubt you'll need to alter Voxelibre or Mineclonia to do it.