Updates to flood simulation end-to-end

[annehaley]

This PR includes the following updates:

• In the flood simulation task, input options for time_period have changed to ['2031-2050', '2041-2060']
• In the network failures task, rather than assuming nodes come back online once the flood recedes, now assume that a node stays offline once it has been flooded. The final timestep of the flood network failure animation now represents the cumulative outages across the duration of the flood.