Flow across edges does not match change in volume

[sjordan29]

@jrutyna - as I showed you last week, there are some weird mis-alignments in HEC RAS output where the change in volume for certain cells calculated directly from the volume values at each timestep does not match the values calculated looking at the flow across all edges of boundary cells. I added a notebook in the sandbox: https://github.com/EcohydrologyTeam/ClearWater-riverine/blob/99-gates/examples/dev_sandbox/99_test_ds_boundary.ipynb

I set up a few functions that you can use to do more testing. The build_cell_dataframe will spit out the change in volume calculated from volume values and the change in volume calculated using the flow across edges. It also calculates the total and % difference between these values, and then spits out a dataframe that shows the percent of timesteps that are above a certain theshold percent (you can modify that with the function). I ran this on ~45k-50k cells and saved the results that shows the percent of timesteps above 0.5% difference and unsaved the results to the network (sent you an email with that location).

This function was kinda slow. I'm sure you could speed it up (probably by saving the results more frequently and clearing not memory at the least) -- just wanted to get it started before I leave for vacation!