buffer_types defines a list of data types used in parallel communication. Each entry specifies: (1) A human-readable name for the data type, (2) The corresponding MPI data type for communication, (3) The Fortran data type (with the appropriate kind), (4) The array rank or shape (e.g., scalar, 1D, 2D, etc.). These types are used for creating allreduce/bcast buffers in MPI operations.