fix(ci): use GCC Toolset 12 on Rocky, install Alpine FFmpeg deps

Linux glibc (Rocky 8):
- Install gcc-toolset-12 for C++20 support (Rocky 8 default GCC 8.x lacks -std=c++20)
- Source toolset enable script before build

Linux musl (Alpine 3.20):
- Install all FFmpeg transitive dependencies required by pkg-config
- Alpine's FFmpeg is compiled with many optional features, all need their dev packages

Author: pproenca

.github/workflows/ci.yml

@@ -72,8 +72,8 @@ jobs:
           # Enable EPEL and CRB (PowerTools) repositories
           dnf install -y epel-release
           dnf config-manager --set-enabled powertools || dnf config-manager --set-enabled crb || true
-          # Install build tools (Python 3.9 for node-gyp compatibility)
-          dnf install -y gcc-c++ make python39 git pkgconfig
+          # Install GCC Toolset 12 for C++20 support (Rocky 8 default GCC is 8.x)
+          dnf install -y gcc-toolset-12 make python39 git pkgconfig
           alternatives --set python3 /usr/bin/python3.9 || true
           # Install FFmpeg via RPMFusion (EPEL doesn't have ffmpeg-devel for Rocky 8)
           dnf install -y https://mirrors.rpmfusion.org/free/el/rpmfusion-free-release-8.noarch.rpm || true
@@ -91,7 +91,10 @@ jobs:
         run: npm install --omit=optional
 
       - name: Build
-        run: npm run build
+        run: |
+          # Enable GCC Toolset 12 for C++20 support
+          source /opt/rh/gcc-toolset-12/enable
+          npm run build
 
       - name: Test
         run: npm test
@@ -105,7 +108,23 @@ jobs:
         node: [20, 22]
     steps:
       - name: Install system dependencies
-        run: apk add --no-cache ffmpeg-dev build-base python3 pkgconfig git nodejs npm
+        run: |
+          # Install build tools and Node.js
+          apk add --no-cache build-base python3 pkgconfig git nodejs npm
+          # Install FFmpeg and all transitive dependencies required by pkg-config
+          # Alpine's FFmpeg is compiled with many optional features, all need their dev packages
+          apk add --no-cache \
+            ffmpeg-dev ffmpeg-libs \
+            x264-dev x265-dev libvpx-dev opus-dev libvorbis-dev lame-dev \
+            dav1d-dev aom-dev libtheora-dev libwebp-dev svt-av1-dev rav1e-dev \
+            libjxl-dev libogg-dev \
+            harfbuzz-dev fribidi-dev fontconfig-dev freetype-dev libass-dev \
+            zlib-dev bzip2-dev openssl-dev libxml2-dev \
+            soxr-dev libdrm-dev \
+            lilv-dev libplacebo-dev vidstab-dev zeromq-dev zimg-dev \
+            libva-dev vdpau-dev libX11-dev \
+            librist-dev srt-dev libssh-dev libbluray-dev openmpt-dev \
+            onevpl-dev || true
 
       - name: Checkout
         uses: actions/checkout@v4