fix: mask_output fvd aggregation

If a output_parameters->stream_output->mask_output file was
configured, the flows, velocities, and depths written to disk are an
erroneous mixture of flows, velocities, and depths. For example, the
flow field for a given feature_id contains values for a mixture of
aggregated flows, velocities, and depths. Not the expected flows.

This patch corrects this behavior so the expected aggregated flows _and_
depths are written. However, I am not certain that velocities are
correctly aggregated. I observed NAN values returned for aggregated
velocities. The `optimized_v_data` subroutine needs to be checked to
ensure velocity values are correctly aggregated.

Author: aaraney

src/troute-network/troute/nhd_io.py

@@ -2336,6 +2336,9 @@ def optimized_agg(merge_flowveldepth_reset):
         all_nex_data['Type'] = 'nex'        
         # Set the new 'Type' column as an index
         all_nex_data = all_nex_data.set_index('Type', append=True)
+
+        # Reindex to (n, f), (n, v), (n, d), ...
+        all_nex_data = all_nex_data.reindex(flowveldepth.columns, axis=1)
 
     else:
         all_nex_data = pd.DataFrame()