cache compiled core

.github/workflows/preview-apk.yml

@@ -45,6 +45,19 @@ jobs:
         with:
           working-directory: jni/deltachat-core-rust
 
+      - name: Get deltachat-core-rust submodule hash
+        id: core-hash
+        run: echo "hash=$(git rev-parse HEAD:jni/deltachat-core-rust)" >> $GITHUB_OUTPUT
+
+      - name: Cache compiled core
+        id: cache-core
+        uses: actions/cache@v4
+        with:
+          path: |
+            jni/arm64-v8a
+            libs/arm64-v8a
+          key: core-arm64-v8a-${{ steps.core-hash.outputs.hash }}-${{ hashFiles('jni/Android.mk', 'jni/Application.mk', 'jni/dc_wrapper.c', 'scripts/ndk-make.sh') }}-ndk-r27
+
       - name: Compile core
         env:
           ANDROID_NDK_ROOT: ${{ steps.setup-ndk.outputs.ndk-path }}