treewide: add linters and apply pending suggestions (#426)

.github/workflows/lint.yml

@@ -0,0 +1,42 @@
+name: Lint
+
+on: pull_request
+
+permissions:
+  contents: read
+
+jobs:
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          extra-conf: |
+            extra-experimental-features = nix-command flakes
+
+      - name: Set up cache
+        uses: DeterminateSystems/magic-nix-cache-action@main
+
+      - name: Install tools
+        run: |
+          flake='github:nixos/nixpkgs/e913ae340076bbb73d9f4d3d065c2bca7caafb16'
+          nix profile install "${flake}#statix"
+          nix profile install "${flake}#deadnix"
+          nix profile install "${flake}#jq"
+  
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run statix
+        run: |
+          statix check --format json |\
+            jq --raw-output '.file as $file | .report[] | .severity as $severity | .diagnostics[] | "::warning file=\($file),line=\(.at.from.line),col=\(.at.from.column)::\(.message)"'
+
+      - name: Run deadnix
+        run: |
+          deadnix --no-lambda-arg --output-format json |\
+            jq --raw-output '.file as $file | .results[] | "::warning file=\($file),line=\(.line),col=\(.column)::\(.message)"'