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/flake-module.nix

@@ -0,0 +1,59 @@
+{
+  self,
+  inputs,
+  ...
+}:
+let
+  inputOverrides = builtins.concatStringsSep " " (
+    builtins.map (input: " --override-input ${input} ${inputs.${input}}") (builtins.attrNames inputs)
+  );
+in
+{
+  perSystem =
+    {
+      pkgs,
+      lib,
+      system,
+      ...
+    }:
+    let
+      jsonDocs = import ./eval-docs.nix {
+        inherit pkgs lib;
+        inherit (self) clanLib;
+      };
+    in
+    {
+      legacyPackages.clan-internals-docs = jsonDocs.optionsJSON;
+
+      # Run: nix-unit --extra-experimental-features flakes --flake .#legacyPackages.x86_64-linux.evalTests-build-clan
+      legacyPackages.evalTests-build-clan = import ./tests.nix {
+        inherit lib;
+        inherit (inputs) nixpkgs;
+        clan-core = self;
+        buildClan = self.clanLib.buildClan;
+      };
+      checks = {
+        lib-build-clan-eval = pkgs.runCommand "tests" { nativeBuildInputs = [ pkgs.nix-unit ]; } ''
+          export HOME="$(realpath .)"
+
+          nix-unit --eval-store "$HOME" \
+            --extra-experimental-features flakes \
+            --show-trace \
+            ${inputOverrides} \
+            --flake ${
+              self.filter {
+                include = [
+                  "flakeModules"
+                  "inventory.json"
+                  "lib"
+                  "machines"
+                  "nixosModules"
+                ];
+              }
+            }#legacyPackages.${system}.evalTests-build-clan
+
+          touch $out
+        '';
+      };
+    };
+}