Replace Python numerical kernels with native C execution

bat/start-backend.sh

@@ -5,6 +5,7 @@ set -u
 SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)"
 REPO_ROOT="$(cd -- "$SCRIPT_DIR/.." && pwd -P)"
 PYTHON_EXE="${SYSTEM_SIMULATION_PYTHON:-$REPO_ROOT/.venv/bin/python}"
+export SIMULATION_NUMERIC_ENGINE="${SIMULATION_NUMERIC_ENGINE:-native}"
 
 if [[ "$PYTHON_EXE" != /* ]]; then
   PYTHON_EXE="$REPO_ROOT/$PYTHON_EXE"