feat: replace webp lib by C libwebp

Avoid having to download anything

.github/workflows/release.yml

@@ -22,6 +22,8 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0 # this is important, otherwise it won't checkout the full tree (i.e. no previous tags)
+      - name: Install libwebp-dev
+        run: sudo apt-get install -y libwebp-dev
       - uses: actions/setup-go@v5
         with:
           go-version: 1.23

.github/workflows/test.yml

@@ -17,6 +17,9 @@ jobs:
         with:
           go-version: '1.23'
 
+      - name: Install libwebp-dev
+        run: sudo apt-get install -y libwebp-dev
+
       - name: Install dependencies
         run: go mod tidy