add build cache action

Signed-off-by: ahuston-0 <aliceghuston@gmail.com>

.github/workflows/flake-health-checks.yml

@@ -15,6 +15,16 @@ jobs:
         os: [ubuntu-latest]
     steps:
       - uses: DeterminateSystems/nix-installer-action@main
+
+      - name: Restore Nix store
+        id: restore
+        uses: nix-community/cache-nix-action@v6
+        with:
+          # save a new cache every time `ci.yaml` changes
+          primary-key: similar-cache-${{ matrix.os }}-individual-${{ hashFiles('flake.lock', '*.nix') }}
+          # otherwise, restore a common cache if and only if it matches the current `ci.yaml`
+          restore-prefixes-first-match: similar-cache-${{ matrix.os }}-common-
+
       - name: Setup Attic cache
         uses: ryanccn/attic-action@v0
         with:
@@ -22,9 +32,13 @@ jobs:
           cache: ${{ secrets.ATTIC_CACHE }}
           token: ${{ secrets.ATTIC_TOKEN }}
           skip-push: "true"
+
       - uses: actions/checkout@v4
+
       - run: nix flake check --accept-flake-config
+
       - run: nix ./utils/attic-push.bash
+
   build-checks:
     name: "Build nix outputs"
     runs-on: ${{ matrix.os }}
@@ -33,6 +47,16 @@ jobs:
         os: [ubuntu-latest]
     steps:
       - uses: DeterminateSystems/nix-installer-action@main
+
+      - name: Restore Nix store
+        id: restore
+        uses: nix-community/cache-nix-action@v6
+        with:
+          # save a new cache every time `ci.yaml` changes
+          primary-key: similar-cache-${{ matrix.os }}-individual-${{ hashFiles('flake.lock', '*.nix') }}
+          # otherwise, restore a common cache if and only if it matches the current `ci.yaml`
+          restore-prefixes-first-match: similar-cache-${{ matrix.os }}-common-
+
       - name: Setup Attic cache
         uses: ryanccn/attic-action@v0
         with:
@@ -40,9 +64,27 @@ jobs:
           cache: ${{ secrets.ATTIC_CACHE }}
           token: ${{ secrets.ATTIC_TOKEN }}
           skip-push: "true"
+
       - uses: actions/checkout@v4
+
       - name: Build all outputs
         run: nix run git+https://nayeonie.com/ahuston-0/flake-update-diff -- --build .
+
       - name: Push to Attic
         run: nix ./utils/attic-push.bash
         continue-on-error: true
+
+      - name: Save Nix store
+        if: steps.restore.outputs.hit == 'false'
+        uses: nix-community/cache-nix-action@v6
+        with:
+          # save a new cache every time `ci.yaml` changes
+          primary-key: similar-cache-${{ matrix.os }}-individual-${{ hashFiles('flake.lock', '*.nix') }}
+          # do purge caches
+          purge: true
+          # purge all versions of the individual cache
+          purge-prefixes: similar-cache-${{ matrix.os }}-individual-
+          # created more than 0 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