Change default slope calculation to least squares

Rather than end points

src/analysis/forecast_twl.py

@@ -173,7 +173,7 @@ def mean_slope_for_site_id(
             profile_z=profile_z,
             top_elevation=row[top_elevation_col],
             btm_elevation=row[btm_elevation_col],
-            method="end_points",
+            method="least_squares",
             top_x=row[top_x_col],
         ),
         axis=1,
@@ -249,7 +249,7 @@ def foreshore_slope_from_profile(profile_x, profile_z, tide, runup_function, **k
         beta_new = slope_from_profile(
             profile_x=profile_x,
             profile_z=profile_z,
-            method="end_points",
+            method="least_squares",
             top_elevation=tide + setup + S_total / 2,
             btm_elevation=tide + setup - S_total / 2,
         )