Improvements to laser envelope solver

[MaxThevenet]

List of useful feature, from most to least urgent.

• Proper handling of multiple plasma species. So far, every species deposits chi as an electron, so with 2 species the results are wrong, which is a strong limitation.
• Accelerate H2D & D2H copies when laser.3d_on_host = 1.
• Improve parallelization when laser.3d_on_host = 1. Currently, in Wait and Notify, I suspect that the ParallelFor copies the data to device memory, although the copy should be from/to a host array (the MPI buffer) to/from a host array (the 3D laser envelope): done in Avoid spurious copies to/from GPU in laser MPI communication pattern #807.
• Line cudaGraphExecDestroy(m_cuda_graph_exe_vcycle[i]); in MultiGrid::~MultiGrid causes an error when running the MG solver in Debug mode on nvidia GPU. This should be fixed, although the simulation runs fine until finalise: done in MultiGrid Solver: More generic type of coefficients #808.
• Option to not evolve the laser phase --> Maxence
• Properly handle Mult and Chi.
• Implement AMD.
• In case this happens: make sure we don't exceed MAX_INT.
• Initialization of a laser profile via the parser (non-Gaussian).
• the possibility to load and restart the laser.
• the possibility to propagate the laser backwards.
• Communicate guard cells? This may account for small differences observed between serial and parallel (1.e-9).
• Fix Array3/Array4 thing. More details needed.
• Separate resolution and bounds for the laser array, as well as multiple lasers --> Maxence.
• Compatible with adaptive time step.