Gazebo broken on develop branch due to removal of freeimage from nixpkgs

Gazebo can no longer be compiled on the develop branch due to freeimage having been removed from nixpkgs. Upstream issues: - gazebosim/gz-rendering#1235 - gazebosim/gz-common#771 - gazebosim/gz-common#388 Related: - NixOS/nixpkgs#454867 - gazebosim/gz-common#590 - #509 - gazebosim/gz-common#725 A possible temporary fix would be to use `freeimage` from the `25.05` nixpkgs channel, or alternatively vendoring freeimage into nix-ros-overlay.