[markov_asset] Update to JAX and runtime comparison

[xuanguang-li]

This pull request modernizes the markov_asset.md notebook by refactoring the codebase to use JAX and JAX NumPy.

• Refactored all numerical computations and linear algebra from numpy and numpy.linalg to jax.numpy and jax.numpy.linalg.
• Replaced the mutable AssetPriceModel class with an immutable, type-safe NamedTuple version and introduced a create_ap_model factory function for consistent construction.
• Updated function signatures and internal logic to use the new model structure.
• Replaced manual Python loops with JAX functional control flow constructs such as jax.lax.while_loop and jax.lax.fori_loop.
• Fixed minor bugs in parameter initialization, state handling, and tolerance defaults.

Update: Runtime Comparison Between JAX (GPU), JAX (CPU), and NumPy

Methodology:

• The JAX version uses the code in this PR, while the NumPy version uses the code in main.
• The runtime for JAX (GPU) is measured using Google Colab.
• Runtime is collected using qe.timeit over 1,000 iterations.
• Each iteration consists of one function that solves the consol price and one that solves the call option price.

Results:

• Average runtime: JAX (CPU) > NumPy > JAX (GPU).
• More details are shown in the attached plots.

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