refactor(wisdom): rename wisdomSimpleSlice to wisdomSlice

Rename the helper function `wisdomSimpleSlice` to `wisdomSlice` across
the codebase and update documentation to reflect the new naming
convention. This change simplifies the API for creating trivial
single-package slices.

modules/desktop/options.nix

@@ -11,7 +11,7 @@
     in
     map (name: self.homeManagerModules.${name}) names;
 
-  flake.lib.wisdomSimpleSlice =
+  flake.lib.wisdomSlice =
     { path, default, description, packages }:
     { config, lib, pkgs, ... }:
     let