Dem_s update in connectivity function call

[erialC-P]

This PR replaces the hydrological SRTM dem layer (dem_h) with the smoothed raw SRTM dem (dem_s) in our connectivity masking function call. The PR swaps the default value in the function call from dem_h to dem_s and updates the explicit use of the function in the intertidal_workflow notebook.
Both layers handle nodata values differently but I have confirmed that the difference does not impact the outputs in the connectivity masking function (figure 1).

This figure details the resulting connectivity masks, calculated using a) dem_h, b) dem_s (applied as per (a), where nodata values form the starting point for the cost-distance mask), d) dem_s, where 0 m elevations are used as the base of the cost-distance mask and c) the (null) difference between (b) and (d), showing that our code produces the same outcomes, regardless of the nodata or 0 m elevation baseline. Consequently, our extents.load_connectivity_mask function call has not been changed to accommodate the new dem input layer.

[robbibt]

Awesome, thanks @erialC-P! I reverted the change to the tests (see comment), but apart from that, looks great!