Restructure IFP lectures: separate transient shocks into new lecture (#747)

* Restructure IFP lectures: separate transient shocks into new lecture

- Split ifp_egm.md into two lectures:
  - ifp_egm.md (III): Simplified model with y(z) = exp(z), no transient shocks
  - ifp_egm_transient_shocks.md (IV): Full model with y(z,eta) and Monte Carlo integration
- Update ifp_advanced.md title from IV to V (Stochastic Returns on Assets)
- Update _toc.yml to include new lecture in sequence
- Increase savings_grid_size to 200 for better accuracy
- Convert utility functions to lambda expressions for conciseness

This reorganization improves pedagogy by introducing EGM with a simpler model first,
then adding complexity with transient shocks in the next lecture.

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

Co-Authored-By: Claude <noreply@anthropic.com>

* Fix duplicate equation labels in ifp_egm_transient_shocks

- Rename equation labels to avoid conflicts with ifp_egm.md:
  - eqst → eqst_ts
  - eqeul1 → eqeul1_ts
  - cfequ → cfequ_ts
- Update all references to use new labels

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

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: jstac

lectures/_toc.yml

@@ -87,6 +87,7 @@ parts:
   - file: ifp_discrete
   - file: ifp_opi
   - file: ifp_egm
+  - file: ifp_egm_transient_shocks
   - file: ifp_advanced
 - caption: LQ Control
   numbered: true

lectures/ifp_advanced.md

@@ -17,7 +17,7 @@ kernelspec:
 </div>
 ```
 
-# {index}`The Income Fluctuation Problem IV: Stochastic Returns on Assets <single: The Income Fluctuation Problem IV: Stochastic Returns on Assets>`
+# {index}`The Income Fluctuation Problem V: Stochastic Returns on Assets <single: The Income Fluctuation Problem V: Stochastic Returns on Assets>`
 
 ```{contents} Contents
 :depth: 2