FluidX3D v2.9 (multithreading)

Thank you for using FluidX3D! The v2.9 update makes simulation startup a lot quicker, especially for large multi-GPU simulations:

• added cross-platform parallel_for implementation in utilities.hpp using std::threads
• significantly (>4x) faster simulation startup with multithreaded geometry initialization and sanity checks
• faster calculate_force_on_object() and calculate_torque_on_object() functions with multithreading
• refactoring
• added total runtime and LBM runtime to lbm.write_status()

Bug fixes:

• fixed bug in voxelization ray direction for re-voxelizing rotating objects
• fixed bug in Mesh::get_bounding_box_size()
• fixed bug in print_message() function in utilities.hpp

Let the cores go brrrr!

Have fun with the software!
-- Moritz