Include agenix module and package directly

Avoids adding an extra flake input only to fetch a single module and
package.

Reviewed-by: Aleix Boné <abonerib@bsc.es>
Tested-by: Rodrigo Arias Mallo <rodrigo.arias@bsc.es>

flake.lock

@@ -1,71 +1,5 @@
 {
   "nodes": {
-    "agenix": {
-      "inputs": {
-        "darwin": "darwin",
-        "home-manager": "home-manager",
-        "nixpkgs": [
-          "nixpkgs"
-        ],
-        "systems": "systems"
-      },
-      "locked": {
-        "lastModified": 1750173260,
-        "narHash": "sha256-9P1FziAwl5+3edkfFcr5HeGtQUtrSdk/MksX39GieoA=",
-        "owner": "ryantm",
-        "repo": "agenix",
-        "rev": "531beac616433bac6f9e2a19feb8e99a22a66baf",
-        "type": "github"
-      },
-      "original": {
-        "owner": "ryantm",
-        "repo": "agenix",
-        "type": "github"
-      }
-    },
-    "darwin": {
-      "inputs": {
-        "nixpkgs": [
-          "agenix",
-          "nixpkgs"
-        ]
-      },
-      "locked": {
-        "lastModified": 1744478979,
-        "narHash": "sha256-dyN+teG9G82G+m+PX/aSAagkC+vUv0SgUw3XkPhQodQ=",
-        "owner": "lnl7",
-        "repo": "nix-darwin",
-        "rev": "43975d782b418ebf4969e9ccba82466728c2851b",
-        "type": "github"
-      },
-      "original": {
-        "owner": "lnl7",
-        "ref": "master",
-        "repo": "nix-darwin",
-        "type": "github"
-      }
-    },
-    "home-manager": {
-      "inputs": {
-        "nixpkgs": [
-          "agenix",
-          "nixpkgs"
-        ]
-      },
-      "locked": {
-        "lastModified": 1745494811,
-        "narHash": "sha256-YZCh2o9Ua1n9uCvrvi5pRxtuVNml8X2a03qIFfRKpFs=",
-        "owner": "nix-community",
-        "repo": "home-manager",
-        "rev": "abfad3d2958c9e6300a883bd443512c55dfeb1be",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nix-community",
-        "repo": "home-manager",
-        "type": "github"
-      }
-    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1752436162,
@@ -84,24 +18,8 @@
     },
     "root": {
       "inputs": {
-        "agenix": "agenix",
         "nixpkgs": "nixpkgs"
       }
-    },
-    "systems": {
-      "locked": {
-        "lastModified": 1681028828,
-        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
-        "owner": "nix-systems",
-        "repo": "default",
-        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nix-systems",
-        "repo": "default",
-        "type": "github"
-      }
     }
   },
   "root": "root",