Alternative options for reading runoff volume arrays

[rileyhales]

Allow options for alternative methods for reading the runoff volumes array.

Runoff volumes array incremental reader generator instead of in memory array

Do you want to read the entire array in memory up front and then route it or do you want to incrementally read from the array/file on disc?

To reduce memory consumption (but maybe be slower?) you can incrementally read from the array if the data are provided in a chunked format that is optimized for it.