Modernize C builds with offline dependencies and portable runtime helpers (#3050)

Bundle pinned offline dependencies, remove libcork/libipset and submodule requirements, and add portable runtime helpers with relocatable static/shared library installations.

Add Clang static build validation for Linux/musl, macOS and Windows, real TCP/UDP and SIP003 interoperability coverage, and recorded performance tradeoffs. All 21 hosted checks pass at the reviewed PR head 8d504e6218.

.github/workflows/build.yml

@@ -15,8 +15,6 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v6
-        with:
-          submodules: recursive
 
       - name: Install dependencies (Linux)
         if: runner.os == 'Linux'
@@ -31,7 +29,7 @@ jobs:
       - name: Build
         run: |
           mkdir -p build && cd build
-          cmake .. -DCMAKE_BUILD_TYPE=Release
+          cmake .. -DCMAKE_BUILD_TYPE=Release -DSS_DEPENDENCY_MODE=system -DWITH_STATIC=OFF
           jobs="$(nproc 2>/dev/null || sysctl -n hw.ncpu)"
           make -j"$jobs"
 
@@ -39,15 +37,13 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
-        with:
-          submodules: recursive
 
       - name: Install dependencies
         run: |
           sudo apt-get update
           sudo apt-get install -y libpcre2-dev libmbedtls-dev libsodium-dev libev-dev libc-ares-dev
           sudo apt-get install -y --no-install-recommends \
-            build-essential debhelper dpkg-dev fakeroot asciidoc-base xmlto pkg-config
+            build-essential cmake debhelper dpkg-dev fakeroot asciidoc-base xmlto pkg-config
 
       - name: Debian package build test
         run: bash tests/test_deb_build.sh