Add Calculations for Self-Diffusivity and Viscosity

MDAnalysis provides minimal support for calculating transport properties, measurable values which define the transfer of mass, heat, momentum, or charge. These properties are vital for biomolecular research and chemical engineering. This project aims to add methods for calculating self-diffusivity and shear viscosity, the two most widely used transport properties in the literature, with three main deliverables: • Construct a class to calculate self-diffusivity via the Green-Kubo method • Build a class to calculate shear viscosity via the Einstein-Helfand method • Test and document the new features thoroughly, ensuring the calculations are reliable and easy to use