ci: Update Nix installation and caching

.github/workflows/ci.yml

@@ -39,12 +39,23 @@ jobs:
         uses: actions/checkout@v4
         with:
           fetch-depth: 0
-      - name: Install Nix and run tests
-        uses: cachix/install-nix-action@v25
+      - uses: cachix/install-nix-action@v25
+      - name: Restore and cache Nix store
+        uses: nix-community/cache-nix-action@v5
         with:
-          nix_path: nixpkgs=channel:nixos-unstable
-      - uses: cachix/cachix-action@v14
-        with:
-          name: peerswap
-          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+          # restore and save a cache using this key
+          primary-key: nix-${{ runner.os }}-${{ hashFiles('**/*.nix') }}
+          # if there's no cache hit, restore a cache by this prefix
+          restore-prefixes-first-match: nix-${{ runner.os }}-
+          # collect garbage until Nix store size (in bytes) is at most this number
+          # before trying to save a new cache
+          gc-max-store-size-linux: 1073741824
+          # do purge caches
+          purge: true
+          # purge all versions of the cache
+          purge-prefixes: cache-${{ runner.os }}-
+          # created more than this number of seconds ago relative to the start of the `Post Restore` phase
+          purge-created: 0
+          # except the version with the `primary-key`, if it exists
+          purge-primary-key: never
       - run: nix-shell --run "make test-${{matrix.test-vector}}"