v1.0.0.0

ci: pin GCC 9 for Linux x64 and arm64 builds

GCC versions > 9 produce broken crypto library output due to
aggressive optimisations. Install gcc-9/g++-9 (x64) and
gcc-9-aarch64-linux-gnu (arm64) and redirect the default gcc/g++
via update-alternatives. Switched arm64 back to cross-compile
from ubuntu-22.04 using linux-arm64-gcc-cross-package preset.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>