feat: implement ruff as flake checks

Had to add `--impure` to the call due to the following error otherwise:

```
error:
       … while checking flake output 'packages'
         at /nix/store/5cjz7jyqyfr5vq8b6bjs24vdnvdhy9rb-source/flake.nix:118:7:
          117|
          118|       packages = forEachSystem (system:
             |       ^
          119|         let

       … while checking the derivation 'packages.x86_64-linux.bootstrap-aarch64'
         at /nix/store/dg3hg3ksr5sl3adskxiwj7357z47ggvr-source/lib/attrsets.nix:977:47:
          976|   */
          977|   nameValuePair = name: value: { inherit name value; };
             |                                               ^
          978|

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: 'builtins.storePath' is not allowed in pure evaluation mode

```

.github/workflows/lints.yml

@@ -5,7 +5,7 @@ on:
   schedule:
     - cron: 0 0 * * 1
 jobs:
-  lint-nix:
+  check:
     runs-on: ubuntu-latest
 
     steps:
@@ -15,21 +15,5 @@ jobs:
       - name: Install nix
         uses: cachix/install-nix-action@v25
 
-      - name: Run nix-formatter-pack-check
+      - name: Run flake checks
-        run: nix build .#checks.x86_64-linux.nix-formatter-pack-check
+        run: nix flake check --impure -L
-
-  lint-py:
-    runs-on: ubuntu-latest
-
-    steps:
-      - name: Checkout repository
-        uses: actions/checkout@v4
-
-      - name: Install nix
-        uses: cachix/install-nix-action@v25
-
-      - name: Run ruff linter
-        run: nix run 'nixpkgs#ruff' -- check
-
-      - name: Run ruff formatter
-        run: nix run 'nixpkgs#ruff' -- format --diff

checks/ruff-fmt.nix

@@ -0,0 +1,10 @@
+{ pkgs, checkRoot }:
+pkgs.runCommandLocal "ruff-fmt"
+{
+  src = ./.;
+  nativeBuildInputs = with pkgs; [ ruff ];
+}
+  ''
+    cd ${checkRoot};
+    ruff format --no-cache --diff && mkdir $out
+  ''

checks/ruff-lint.nix

@@ -0,0 +1,10 @@
+{ pkgs, checkRoot }:
+pkgs.runCommandLocal "ruff-lint"
+{
+  src = ./.;
+  nativeBuildInputs = with pkgs; [ ruff ];
+}
+  ''
+    cd ${checkRoot};
+    ruff check --no-cache && mkdir $out
+  ''

flake.nix

@@ -63,9 +63,16 @@
         };
       });
 
-      checks = forEachSystem (system: {
+      checks = forEachSystem (system:
+        let
+          pkgs = import nixpkgs { inherit system; };
+        in
+        {
           nix-formatter-pack-check = nix-formatter-pack.lib.mkCheck formatterPackArgsFor.${system};
-      });
+          ruff-lint = import ./checks/ruff-lint.nix { inherit pkgs; checkRoot = ./.; };
+          ruff-fmt = import ./checks/ruff-fmt.nix { inherit pkgs; checkRoot = ./.; };
+        }
+      );
 
       formatter = forEachSystem (system: nix-formatter-pack.lib.mkFormatter formatterPackArgsFor.${system});