River states should be updated in-place,

[odunbar]

Issue

ClimaRivers.jl/src/Routing.jl

Line 25 in cc1714a

river_state = compute_river_state(date_window, river_model, env)

We create new states at every iterating time-step during integration of the river model. This may be quite expensive (see the PR #24)

Possible solution

• Overwrite the state by default using in-place updates.
• Create a diagnostic interface to create a full state (history) copy to save at allocated frequency/dates
• Creation of some simple reduced file output of e.g. streamflow-per-basin that can be used for plotting etc.