consider writing outputs incrementally (per timestep)

[andywood]

Currently GMET's spatial regression writes no output until the entire run is done. If a run dies before the final timestep is processed, all output is lost.

Letting GMET write each timestep after the regression is complete would also reduce the size of the memory arrays needed -- right now large GMET domains can require using big-memory nodes to complete.

There would be a slight run time hit but not much.