Simplify McCall model: Compute reservation wage directly from value function

This commit simplifies the job search model by eliminating the intermediate policy array and computing the reservation wage directly from the value function.

Key changes:
- Removed `get_greedy` function entirely
- Modified `get_reservation_wage` to compute directly from value function v_u
- Updated `update_agent` to use reservation wage (scalar) instead of policy array
- Updated all simulation functions to work with reservation wage

Benefits:
- Simpler, more intuitive code
- More efficient (no need to store full policy array)
- Clearer conceptually (directly compute and use the threshold)

The reservation wage is now computed by finding the lowest wage where:
accept value >= reject value, which directly implements the optimal policy.

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

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

Author: jstac