Fix AMD64 FFI crash by using native AMD64 runners

The AMD64 builds were crashing due to cross-compilation. Blacksmith runners
are ARM64, so when building linux/amd64 on them, Docker uses QEMU emulation
which breaks the C FFI code in native/snmp_helper.c.

Solution:
- AMD64 builds now use GitHub's ubuntu-latest runners (native x86_64)
- ARM64 builds continue using Blacksmith ARM64 runners (native)
- Both architectures now build natively, eliminating FFI segfaults

.github/workflows/ci.yml

@@ -169,10 +169,10 @@ jobs:
         include:
           - platform: linux/amd64
             arch: amd64
-            runner: blacksmith-4vcpu-ubuntu-2404
+            runner: ubuntu-latest  # Use GitHub's native AMD64 runners
           - platform: linux/arm64
             arch: arm64
-            runner: blacksmith-4vcpu-ubuntu-2404-arm
+            runner: blacksmith-4vcpu-ubuntu-2404-arm  # Use Blacksmith ARM64 runners
     steps:
       - name: Checkout
         uses: actions/checkout@v4