lib: move clan out of lib into flake

This allows clanLib to stay agnostic and be more testable

lib/clan/default.nix

@@ -0,0 +1,52 @@
+## WARNING: Do not add core logic here.
+## This is only a wrapper such that 'clan' can be called as a function.
+{
+  lib,
+  clan-core,
+}:
+/**
+  Function that takes clan options as function arguments.
+
+  It behaves equivalent to:
+
+  ```nix
+  {
+    imports = [
+      clan-core.modules.clan.default
+      args
+    ];
+  }
+  ```
+
+  Arguments:
+
+  - self: Reference to the current flake. This is required be passed.
+  - ...: All other arguments - Which are options as of the 'clan.*' module
+
+  Returns:
+  The clan configuration.
+*/
+{
+  self ? lib.warn "Argument: 'self' must be set" null, # Reference to the current flake
+  ...
+}@m:
+let
+  nixpkgs = self.inputs.nixpkgs or clan-core.inputs.nixpkgs;
+  nix-darwin = self.inputs.nix-darwin or clan-core.inputs.nix-darwin;
+in
+lib.evalModules {
+  class = "clan";
+  specialArgs = {
+    inherit
+      self
+      ;
+    inherit
+      nixpkgs
+      nix-darwin
+      ;
+  };
+  modules = [
+    clan-core.modules.clan.default
+    m
+  ];
+}