use np.concat to avoid copies

Co-authored-by: @neutrinoceros

Author: DanielYang59

cmasher/utils.py

@@ -305,24 +305,18 @@ def combine_cmaps(
 
     # Generate default nodes for equal separation
     if nodes is None:
-        nodes_arr = np.linspace(0, 1, len(_cmaps) + 1)[1:-1]
-    elif isinstance(nodes, list):
-        nodes_arr = np.array(nodes)
-    elif isinstance(nodes, np.ndarray):
-        nodes_arr = nodes
+        nodes_arr = np.linspace(0, 1, len(_cmaps) + 1)
+    elif isinstance(nodes, (list, np.ndarray)):
+        nodes_arr = np.concatenate([[0.0], nodes, [1.0]])
     else:
         raise TypeError(f"Unsupported nodes type: {type(nodes)}.")
 
     # Check nodes length
-    if len(nodes_arr) != len(_cmaps) - 1:
+    if len(nodes_arr) != len(_cmaps) + 1:
         raise ValueError(
             "Number of nodes should be one less than the number of colormaps."
         )
 
-    # Insert the start/end points to make segmenting easier
-    nodes_arr = np.insert(nodes_arr, 0, 0.0)
-    nodes_arr = np.append(nodes_arr, 1.0)
-
     # Check node values
     if any((nodes_arr < 0) | (nodes_arr > 1)) or any(np.diff(nodes_arr) <= 0):
         raise ValueError(