Refactor(build-clan): rename to lib/modules

This is a preparation for moving everything into clan, to make it all one module evaluation

lib/modules/default.nix

@@ -0,0 +1,83 @@
+## WARNING: Do not add core logic here.
+## This is only a wrapper such that buildClan can be called as a function.
+## Add any logic to ./module.nix
+{
+  lib,
+  clanLib,
+  ...
+}:
+{
+  flakePartsModule = {
+    imports = [
+      (lib.modules.importApply ./interface.nix { inherit clanLib; })
+      ./module.nix
+    ];
+  };
+
+  /**
+    A function that takes some arguments such as 'clan-core' and returns the 'buildClan' function.
+
+    # Arguments of the first function
+    - clan-core: Self, provided by our flake-parts module
+    - publicAttrs: { clan :: List Str, topLevel :: List Str } Publicly exported attribute names
+
+    # Arguments of the second function (aka 'buildClan')
+    - self: Reference to the users flake
+    - inventory: An "Inventory" attribute set, see the docs, for how to construct one
+    - specialArgs: Extra arguments to pass to nixosSystem i.e. useful to make self available
+    - ...: Any other argument of the 'clan' submodule. See the docs for all available options
+
+    # Returns
+
+    Public attributes of buildClan. As specified in publicAttrs.
+  */
+  buildClanWith =
+    {
+      clan-core,
+      # TODO: Below should be module options such that the user can override them?
+      nixpkgs,
+      publicAttrs ? import ./public.nix,
+      nix-darwin ? null,
+    }:
+    {
+      ## Inputs
+      self ? lib.warn "Argument: 'self' must be set when using 'buildClan'." null, # Reference to the current flake
+      # allows to include machine-specific modules i.e. machines.${name} = { ... }
+      # A map from arch to pkgs, if specified this nixpkgs will be only imported once for each system.
+      # This improves performance, but all nipxkgs.* options will be ignored.
+      # deadnix: skip
+      inventory ? { },
+      ## Special inputs (not passed to the module system as config)
+      specialArgs ? { }, # Extra arguments to pass to nixosSystem i.e. useful to make self available
+      ##
+      ...
+    }@attrs:
+    let
+      eval = import ./function-adapter.nix {
+        inherit
+          lib
+          nixpkgs
+          nix-darwin
+          clan-core
+          self
+          ;
+        inherit specialArgs;
+      };
+      rest = builtins.removeAttrs attrs [ "specialArgs" ];
+      result = eval {
+        imports = [
+          rest
+          # implementation
+          ./module.nix
+        ];
+      };
+    in
+    {
+      clan = lib.genAttrs publicAttrs.clan (
+        name:
+        result.clanInternals.${name}
+          or (throw "Output: clanInternals.${name} not found. Check: ${result.file}")
+      );
+    }
+    // lib.filterAttrs (name: _v: builtins.elem name publicAttrs.topLevel) result;
+}