Fix aarch64 Linux cross-build by provisioning target zlib and restoring cross-build matrix

[Copilot]

The failing linux-cross-build (aarch64-unknown-linux-gnu, true) job was caused by missing target-arch zlib in the cross container (ZLIB_LIBRARY not found during CMake configure). This change restores the Linux cross-build workflow path and ensures required aarch64 zlib dev packages are installed before build.

• CI workflow updates

  • Restored the linux-cross-build job in .github/workflows/rust.yml with matrix targets:
    • aarch64-unknown-linux-gnu (via cross)
    • x86_64-unknown-linux-gnu (native cargo build)
  • Kept target-specific dependency install behavior aligned with each path.

• Cross container dependency provisioning

  • Added Cross.toml with target-specific pre-build for aarch64-unknown-linux-gnu.
  • Installs zlib1g-dev:$CROSS_DEB_ARCH inside the cross image so CMake resolves ZLIB_LIBRARY for wxWidgets/wxdragon-sys configuration.

• Workflow token hardening

  • Added top-level workflow permissions:
    • contents: read

[target.aarch64-unknown-linux-gnu]
pre-build = [
  "dpkg --add-architecture $CROSS_DEB_ARCH",
  "apt-get update && apt-get --assume-yes install zlib1g-dev:$CROSS_DEB_ARCH",
]