Fix missing random module import in need_for_speed.md

Add missing `import random` statement to fix NameError when running
the vectorization example code that uses random.uniform().

Tested by converting to Python with jupytext and running successfully.

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Co-Authored-By: Claude <[email protected]>

Author: jstac

lectures/need_for_speed.md

@@ -63,6 +63,7 @@ Let's start with some imports:
 import numpy as np
 import quantecon as qe
 import matplotlib.pyplot as plt
+import random
 ```