lib: mkOfflineFlakeLock init

copied from the clan-core-flake module

I plan to re-use this function to improve the clan test framework to allow cli execution

pkgs/clan-core-flake/flake-module.nix

@@ -1,47 +1,15 @@
-{ self, inputs, ... }:
+{ self, ... }:
+let
+  inherit (self.clanLib.flakes)
+    mkOfflineFlakeLock
+    ;
+in
 {
   perSystem =
     {
-      lib,
       pkgs,
       ...
     }:
-    let
-      # A flake lock for offline use.
-      # All flake inputs are locked to an existing store path
-      clanCoreLockFile =
-        clanCore:
-        let
-          flakeLock = lib.importJSON (clanCore + "/flake.lock");
-          flakeInputs = builtins.removeAttrs inputs [ "self" ];
-          flakeLockVendoredDeps =
-            flakeLock:
-            flakeLock
-            // {
-              nodes =
-                flakeLock.nodes
-                // (lib.flip lib.mapAttrs flakeInputs (
-                  name: _:
-                  # remove follows and let 'nix flake lock' re-compute it later
-                  # (lib.removeAttrs flakeLock.nodes.${name} ["inputs"])
-                  flakeLock.nodes.${name}
-                  // {
-                    locked = {
-                      inherit (flakeLock.nodes.${name}.locked) narHash;
-                      lastModified =
-                        # lol, nixpkgs has a different timestamp on the fs???
-                        if name == "nixpkgs" then 0 else 1;
-                      path = "${inputs.${name}}";
-                      type = "path";
-                    };
-                  }
-                ));
-            };
-          clanCoreLock = flakeLockVendoredDeps flakeLock;
-          clanCoreLockFile = builtins.toFile "clan-core-flake.lock" (builtins.toJSON clanCoreLock);
-        in
-        clanCoreLockFile;
-    in
     {
       packages.clan-core-flake =
         let
@@ -65,7 +33,7 @@
                 export NIX_STORE_DIR=$HOME
                 cp -r ${clanCore} $out
                 chmod +w -R $out
-                cp ${clanCoreLockFile clanCore} $out/flake.lock
+                cp ${mkOfflineFlakeLock clanCore} $out/flake.lock
                 nix flake lock $out --extra-experimental-features 'nix-command flakes'
                 clanCoreHash=$(nix hash path ${clanCore} --extra-experimental-features 'nix-command')
               '';