feat(ci): generate package size report

We should keep it lean c:

.forgejo/workflows/check.yml

@@ -13,3 +13,16 @@ jobs:
       - uses: https://git.salame.cl/actions/checkout@v4
       - run: nix --version
       - run: nix flake check --keep-going --verbose --print-build-logs
+  report-size:
+    runs-on: nixos
+    needs: build
+    steps:
+      - uses: https://git.salame.cl/actions/checkout@v4
+      - run: nix --version
+      - name: Generate size report
+        uses: https://git.salame.cl/jalil/nix-flake-outputs-size@main
+        with:
+          comment-on-pr: ${{ github.ref_name != 'main' }}
+          generate-artifact: ${{ github.ref_name == 'main' }}
+          do-comparison: true
+          job-name: report-size