Convert wealth_dynamics lecture from Numba to JAX

- Add JAX imports and GPU acceleration warning
- Convert @jitclass WealthDynamics to NamedTuple + factory pattern
- Replace @jit functions with pure JAX functions using jax.lax.scan
- Implement explicit JAX random key management
- Update all application code and exercises to use JAX implementation
- Follow QuantEcon JAX style guide rules for functional programming

Author: mmcky