refactor(ops/nixos): Move my NixOS configurations to //users/tazjin

NixOS modules move one level up because it's unlikely that //ops/nixos
will contain actual systems at this point (they're user-specific).

This is the first users folder, so it is also added to the root
readTree invocation for the repository.

Change-Id: I546c701145fa204b7ba7518a8a56a783588629e0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/244
Reviewed-by: tazjin <mail@tazj.in>

bin/__dispatch.sh

@@ -36,7 +36,7 @@ case "${TARGET_TOOL}" in
     attr="third_party.age"
     ;;
   rebuilder)
-    attr="ops.nixos.rebuilder"
+    attr="users.tazjin.nixos.rebuilder"
     ;;
   meson)
     attr="third_party.meson"