Fixing index_search to support particles exactly at right side

Author: erikvansebille

src/parcels/_core/index_search.py

@@ -44,7 +44,7 @@ def _search_1d_array(
     # TODO v4: We probably rework this to deal with 0D arrays before this point (as we already know field dimensionality)
     if len(arr) < 2:
         return np.zeros(shape=x.shape, dtype=np.int32), np.zeros_like(x)
-    index = np.searchsorted(arr, x, side="right") - 1
+    index = np.clip(np.searchsorted(arr, x, side="right") - 1, 0, len(arr) - 2)
     # Use broadcasting to avoid repeated array access
     arr_index = arr[index]
     arr_next = arr[np.clip(index + 1, 1, len(arr) - 1)]  # Ensure we don't go out of bounds
@@ -57,7 +57,7 @@ def _search_1d_array(
     # bcoord = (x - arr[index]) / dx
 
     index = np.where(x < arr[0], LEFT_OUT_OF_BOUNDS, index)
-    index = np.where(x >= arr[-1], RIGHT_OUT_OF_BOUNDS, index)
+    index = np.where(x > arr[-1], RIGHT_OUT_OF_BOUNDS, index)
 
     return np.atleast_1d(index), np.atleast_1d(bcoord)