Store motif letter counts with Python floats

This adds a cast to avoid storing numpy floats
which as of numpy 2.0 have a different __repr__
and this complicate our doctest behaviour.

Closes #4676.

Bio/motifs/matrix.py

@@ -32,7 +32,8 @@ def __init__(self, alphabet, values):
                 self.length = len(values[letter])
             elif self.length != len(values[letter]):
                 raise Exception("data has inconsistent lengths")
-            self[letter] = list(values[letter])
+            # Cast any numpy floats into Python floats:
+            self[letter] = [float(_) for _ in values[letter]]
         self.alphabet = alphabet
 
     def __str__(self):