Changed Infection to keep reference to VariantParameters instance instead of the name of the variant
Also made variant required for the infection process, and moved the random variant initialization logic from deep inside the Infection, to up top as part of the simulation initialization.
Changed Infection to keep reference to VariantParameters instance instead of the name of the variant Also made variant required for the infection process, and moved the random variant initialization logic from deep inside the Infection, to up top as part of the simulation initialization.