CI/Nix: add cache-nix-action

Use nixbuild/nix-quick-install-action which pairs well with
nix-community/cache-nix-action.

Should help with build times by reducing the number of packages needing
to be re-downloaded on each run.

Parameters are taken from https://github.com/nix-community/cache-nix-action
and may be tweaked later.

.github/workflows/nix-build.yaml

@@ -10,17 +10,41 @@ jobs:
       uses: actions/checkout@v3
       with:
         submodules: recursive
-    - name: Install nix
-      uses: cachix/install-nix-action@v20
+
+    - name: Install Nix
+      uses: nixbuild/nix-quick-install-action@v31
       with:
-        install_url: https://nixos.org/nix/install
-        extra_nix_config: |
-          auto-optimise-store = true
-          access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
-          experimental-features = nix-command flakes
+        nix_conf: |
+          keep-env-derivations = true
+          keep-outputs = true
+
+    - name: Restore and save Nix store
+      uses: nix-community/cache-nix-action@v6
+      with:
+        # restore and save a cache using this key
+        primary-key: nix-${{ runner.os }}-${{ hashFiles('**/*.nix', '**/flake.lock') }}
+        # if there's no cache hit, restore a cache by this prefix
+        restore-prefixes-first-match: nix-${{ runner.os }}-
+        # collect garbage until the Nix store size (in bytes) is at most this number
+        # before trying to save a new cache
+        # 1G = 1073741824
+        gc-max-store-size-linux: 1G
+        # do purge caches
+        purge: true
+        # purge all versions of the cache
+        purge-prefixes: nix-${{ runner.os }}-
+        # created more than this number of seconds ago
+        purge-created: 0
+        # or, last accessed more than this number of seconds ago
+        # relative to the start of the `Post Restore and save Nix store` phase
+        purge-last-accessed: 0
+        # except any version with the key that is the same as the `primary-key`
+        purge-primary-key: never
+
     - uses: cachix/cachix-action@v12
       with:
         name: hyprland
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+
     - name: Build Hyprpaper with default settings
       run: nix build --print-build-logs --accept-flake-config