Add CI for 2025 (#63)

Author: kfarnung

.github/workflows/2025.yml

@@ -0,0 +1,32 @@
+name: Advent of Code 2025
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - .github/workflows/2025.yml
+      - 2025/**
+  pull_request:
+    paths:
+      - .github/workflows/2025.yml
+      - 2025/**
+
+jobs:
+  build-2025:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: "2025"
+
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          token: ${{ secrets.PAT }}
+          submodules: true
+
+      - name: Build
+        run: cargo build
+
+      - name: Test
+        run: cargo test