Convert to flake-parts & easy-hosts. Users broke

convert to using flake-parts and easy-hosts for the flake system. This
allows me to remove my poor file-system based code and replace it with
the code done in easy-hosts. Which also has good knock-on effects.

This change factors users out of hosts, which is probably a good change
since users aren't a nixos-module, but aren't completely untangled
either.

I'm going to leave users broken for a minute as I decide exactly how I
want to handle them.

hosts/juri/users/badtz/user.nix

@@ -1,10 +0,0 @@
-{ config, pkgs, ... }:
-
-{
-  fish.enable = true;
-  git = {
-    enable = true;
-    username = "Badtz";
-    email = "may@badtz.dev";
-  };
-}

hosts/juri/users/pan/user.nix

@@ -1,16 +0,0 @@
-{ config, pkgs, ... }:
-
-{
-  fish.enable = true;
-  git = {
-    enable = true;
-    username = "Julia Lange";
-    email = "public@julialange.org";
-  };
-  neovim = {
-    enable = true;
-    themes.catppuccin.enable = true;
-  };
-  lf.enable = true;
-  zoxide.enable = true;
-}