Migrate to nix-fast-build and update inputs

.github/actions/attic-cache/action.yml

@@ -1,15 +0,0 @@
-name: "Attic Watch and Push"
-description: "Composite action pushes results after the job completes. Needs prior attic-cache action to have executed successfully."
-
-inputs:
-  cache_repository:
-    description: "Cache repository to use with attic"
-    required: true
-
-runs:
-  using: "composite"
-  steps:
-    - name: Attic Push Results
-      shell: "nix shell nixpkgs#attic-client --command {0}"
-      run: |
-        attic push "${{ inputs.cache_repository }}" "./result" # TODO: Make this smarter

.github/workflows/ci.yml

@@ -27,13 +27,6 @@ jobs:
           attic_auth_token: ${{ secrets.ATTIC_AUTH_TOKEN }}
           cache_repository: fabianhauser:dotfiles
 
-      - name: Build
-        run: nix build --max-jobs 12 --cores 12
-
       - name: Run Checks
-        run: nix flake check
-
-      - name: Setup Cache Push
-        uses: ./.github/actions/attic-cache-push
-        with:
-          cache_repository: fabianhauser:dotfiles
+        shell: nix develop --command bash -c "{0}"
+        run: nix-fast-build --skip-cached --attic-cache fabianhauser:dotfiles