feat: move from npins to lon

lon.nix

@@ -0,0 +1,41 @@
+# Generated by lon. Do not modify!
+let
+
+  lock = builtins.fromJSON (builtins.readFile ./lon.lock);
+
+  # Override with a path defined in an environment variable. If no variable is
+  # set, the original path is used.
+  overrideFromEnv =
+    name: path:
+    let
+      replacement = builtins.getEnv "LON_OVERRIDE_${name}";
+    in
+    if replacement == "" then
+      path
+    else
+    # this turns the string into an actual Nix path (for both absolute and
+    # relative paths)
+    if builtins.substring 0 1 replacement == "/" then
+      /. + replacement
+    else
+      /. + builtins.getEnv "PWD" + "/${replacement}";
+
+  fetchSource =
+    args@{ fetchType, ... }:
+    if fetchType == "git" then
+      builtins.fetchGit {
+        inherit (args) url;
+        ref = args.branch;
+        rev = args.revision;
+        narHash = args.hash;
+      }
+    else if fetchType == "tarball" then
+      builtins.fetchTarball {
+        inherit (args) url;
+        sha256 = args.hash;
+      }
+    else
+      builtins.throw "Unsupported source type ${fetchType}";
+
+in
+builtins.mapAttrs (name: args: overrideFromEnv name (fetchSource args)) lock.sources