Scheduling the steps to take with MCMCSchedule

mutable struct MCMCSchedule
    num_mcmc_steps::Int64
    num_updates::Int64
    start::NamedTuple{(:mcmciter, :pidx),Tuple{Int64,Int64}}
    exclude_updates::DefaultDict{Int64,OrdinalRange{Int64,Int64},UnitRange{Int64}}
end

An object used for iterating over the steps of MCMC samplers. num_mcmc_steps is the total number of MCMC steps, whereas num_updates is a total number of separate updates that can be performed in a single MCMC step. Not all of those updates have to be performed and the pattern of excluding the updates is stored in exclude_updates. The num_updates and exclude_updates can change in the midst of iterating through the MCMCSchedule and the iterator will register that and act accordingly.