ci: cache Maven repository in GitHub Actions

Cache Maven repo to avoid downloading artifacts each run

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dfa1

.github/workflows/ci.yml

@@ -19,6 +19,14 @@ jobs:
           distribution: zulu
           java-version: '25'
 
+      - name: Cache Maven repository
+        uses: actions/cache@v4
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+          restore-keys: |
+            ${{ runner.os }}-maven-
+
       - name: Install protobuf compiler
         run: sudo apt-get install -y protobuf-compiler