Complete Job Search IV lecture: Add utility function and fitted VFI implementation

Updated mccall_fitted_vfi.md to implement the continuous wage offer model with CRRA utility.

Key changes:
- Added CRRA utility function u(c, γ) = (c^(1-γ) - 1)/(1-γ) to mathematical formulation
- Updated Model class to include ρ, ν, and γ parameters
- Implemented Monte Carlo integration for computing conditional expectations (Pv_u)(w)
- Updated Bellman operator T() to use u(w, γ) and u(c, γ)
- Added get_greedy() function for computing optimal policy
- Fixed all model unpacking throughout code
- Implemented compute_expectation() using w' = w^ρ * exp(ν * z) with standard normal draws
- Added Exercise 3: Exploring reservation wage as function of risk aversion γ
- Reformatted text: each sentence on separate line for better version control

Mathematical consistency:
- Code now matches theory where wages and unemployment compensation enter through utility function
- Monte Carlo approximation: (Pv_u)(w) ≈ (1/N) Σ v_u(w^ρ exp(ν z_i))
- Proper JAX implementation with interpolation for fitted value function iteration

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: jstac