Remove support for resetting cumulatives from BMI

[visr]

The coupler is switching to an approach where they don't need to reset the cumulatives to 0. Since this complicated the Ribasim code, let's get rid of it.

The reason for the coupler to move away from resetting cumulatives is that this possibly broke with #1819.

The dedicated BMI arrays like vertical_flux_bmi and user_demand.realized_bmi are removed. The BMI.get_value_ptr now just points to the cumulative state, or if it is not a state (drainage, precipitation) to basin.cumulative_drainage or basin.cumulative_precipitation.

This is breaking because I also renamed these BMI variables to be more consistent with the current code, where we use the term cumulative internally.

user_demand.realized -> user_demand.inflow
basin.drainage_integrated -> basin.cumulative_drainage
basin.infiltration_integrated ->  basin.cumulative_infiltration

[evetion]

Nit: Realized seemed better than inflow. And it seems integrated vs cumulative is math vs non-math coders (I used similar wordings in my concentration PR), but we should come to an agreement for future internal documentation.