ci: enable caching of npm modules

Note: `npm ci` is always required because it's the npm cache that is cached, not the node_modules/ directory.

Reference: https://github.com/actions/setup-node

.github/workflows/build-examples.yml

@@ -37,6 +37,7 @@ jobs:
         uses: actions/setup-node@v6
         with:
           node-version: 20
+          cache: npm
 
       - name: Build ${{ matrix.example }}
         run: |

.github/workflows/ci-browser.yml

@@ -26,6 +26,7 @@ jobs:
         uses: actions/setup-node@v6
         with:
           node-version: 20
+          cache: npm
 
       - name: Install dependencies
         run: npm ci

.github/workflows/ci.yml

@@ -55,6 +55,7 @@ jobs:
         uses: actions/setup-node@v6
         with:
           node-version: ${{ matrix.node-version }}
+          cache: npm
 
       - name: Install dependencies
         run: npm ci

.github/workflows/publish.yml

@@ -24,6 +24,7 @@ jobs:
         with:
           node-version: 24
           registry-url: 'https://registry.npmjs.org'
+          cache: npm
 
       - name: Install dependencies
         run: npm ci