FIX array immutability example

[clijo]

The original example in Exercise 1 of 01 - JAX AI Stack.ipynb assigned the result to a new variable (a_sol_new_ref), leaving the original variable (a_sol) and its binding strictly unchanged:

a_sol_new_ref = a_sol + 1 # This creates a new array and rebinds the Python variable.

This fails to demonstrate anything about the mutability of the original object.

Fix: I have changed this to:

a_sol += 1 # This creates a new array and rebinds the variable `a_sol`.
# a_sol = a_sol + 1  # same as above line, an out-of-place update.
new_a_id_sol = id(a_sol)

Because += would be the syntax for in-place update for NumPy arrays. I have also added a code block demonstrating how the id would be unchanged in NumPy with an in-place update:

import numpy as np 
a = np.random.random((2,2))
original_id = id(a)
a += 1 
new_id = id(a)
print(f"(NumPy, in-place update) IDs are different? {original_id != new_id}")

# One can also do an out-of-place update:
a = a + 1
new_id_out = id(a)
print(f"(NumPy, out-of-place update) IDs are different? {original_id != new_id_out}")