Simplify storage Dict keys

[charleskawczynski]

Right now, the storage Dict keys are entire ScheduledDiagnostics:

julia> keys(integrator.callback.discrete_callbacks[6].affect!.diagnostics_handler.storage)
KeySet for a Dict{ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic, ClimaCore.Fields.Field} with 74 entries. Keys:
  ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic{ClimaDiagnostics.Schedules.EveryDtSchedule{Float64}, ClimaDiagnostics.Schedules.DivisorSchedule, ClimaDiagnostics.Writers.NetCDFWriter{Tuple{Int64, Int64, Int64}, Array{Float64, 3}, Dict{ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic, Array}, ClimaDiagno…
  ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic{ClimaDiagnostics.Schedules.EveryDtSchedule{Float64}, ClimaDiagnostics.Schedules.DivisorSchedule, ClimaDiagnostics.Writers.NetCDFWriter{Tuple{Int64, Int64, Int64}, Array{Float64, 3}, Dict{ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic, Array}, ClimaDiagno…
  ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic{ClimaDiagnostics.Schedules.EveryDtSchedule{Float64}, ClimaDiagnostics.Schedules.DivisorSchedule, ClimaDiagnostics.Writers.NetCDFWriter{Tuple{Int64, Int64, Int64}, Array{Float64, 3}, Dict{ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic, Array}, ClimaDiagno…
  ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic{ClimaDiagnostics.Schedules.EveryDtSchedule{Float64}, ClimaDiagnostics.Schedules.DivisorSchedule, ClimaDiagnostics.Writers.NetCDFWriter{Tuple{Int64, Int64, Int64}, Array{Float64, 3}, Dict{ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic, Array}, ClimaDiagno…
  ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic{ClimaDiagnostics.Schedules.EveryDtSchedule{Float64}, ClimaDiagnostics.Schedules.DivisorSchedule, ClimaDiagnostics.Writers.NetCDFWriter{Tuple{Int64, Int64, Int64}, Array{Float64, 3}, Dict{ClimaDiagnostics.ScheduledDiagnostics.ScheduledDiagnostic, Array}, Cli

I think that we can get closure to fixing the inference issues if we first simplify how we look up which diagnostic is to be computed.

[Sbozzolo]

It's not just storage, it's all the dictionaries in DiagnosticsHandler. I made them dictionaries because not all diagnostics need accumulators and counters, so it was the easiest. I think we could turn them into vectors by adding some more bookkeeping.

[charleskawczynski]

Ok, sounds good, I'll update the PR.