Use float64 in astype to ensure working on 32-bit platforms

Author: jni

src/skan/csr.py

@@ -525,7 +525,7 @@ def __init__(
         if np.issubdtype(skeleton_image.dtype, np.floating):
             self.pixel_values = skeleton_image[coords]
         elif np.issubdtype(skeleton_image.dtype, np.integer):
-            self.pixel_values = skeleton_image.astype(float)[coords]
+            self.pixel_values = skeleton_image.astype(np.float64)[coords]
         else:
             self.pixel_values = None
         self.graph = graph