SPDX license format (#2667)

* Switch to SPDX license format for all non-codegen files

* Add test to ensure all committed JS files have SPDX header

.github/workflows/nodejs.yml

@@ -83,6 +83,9 @@ jobs:
         run: |
           npm run license-checker
 
+      - name: SPDX header check
+        run: npm run license-header
+
   test-bun:
     name: Test Bun
     runs-on: ${{ matrix.os }}