treewide: use inherit for attribute assignments

This change converts redundant attribute assignments of the form `a =
a;` or `a = someSet.a;` into cleaner `inherit` statements. This reduces
verbosity and follows common Nix style for bringing attributes into
scope.

Statix Codes: W03 (manual_inherit), W04 (manual_inherit_from)

Also include statix and the rule in our configuration.

docs/default.nix

@@ -153,11 +153,15 @@ let
           config = lib.listToAttrs (map poisonAttr (lib.filter (n: n != "_module") (lib.attrNames options)));
         };
 
-      options =
-        (docsLib.evalModules {
-          modules = modules ++ [ poisonModule ];
-          class = "homeManager";
-        }).options;
+      inherit
+        (
+          (docsLib.evalModules {
+            modules = modules ++ [ poisonModule ];
+            class = "homeManager";
+          })
+        )
+        options
+        ;
     in
     pkgs.buildPackages.nixosOptionsDoc (
       {

docs/flake.nix

@@ -75,8 +75,7 @@
           pkgs = nixpkgs.legacyPackages.${system};
           docs = import ./default.nix {
             inherit pkgs lib;
-            release = releaseInfo.release;
-            isReleaseBranch = releaseInfo.isReleaseBranch;
+            inherit (releaseInfo) isReleaseBranch release;
           };
         in
         {