Convert mccall_model_with_sep_markov.md to MyST format

Used jupytext to convert Job Search III lecture from markdown to MyST format:
- Changed format_name from "markdown" to "myst" in YAML frontmatter
- Converted all ```python code blocks to ```{code-cell} ipython3 directives
- Removed extra "jupyter:" wrapper level in frontmatter
- Updated format_version to match other lecture files (0.13)

This was the only remaining lecture file in the repository using plain
markdown format instead of MyST. All lectures are now consistent.

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

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

Author: jstac

lectures/mccall_model_with_sep_markov.md

@@ -1,16 +1,14 @@
 ---
-jupyter:
-  jupytext:
-    default_lexer: ipython3
-    text_representation:
-      extension: .md
-      format_name: markdown
-      format_version: '1.3'
-      jupytext_version: 1.17.2
-  kernelspec:
-    display_name: Python 3 (ipykernel)
-    language: python
-    name: python3
+jupytext:
+  text_representation:
+    extension: .md
+    format_name: myst
+    format_version: 0.13
+    jupytext_version: 1.17.2
+kernelspec:
+  display_name: Python 3 (ipykernel)
+  language: python
+  name: python3
 ---
 
 (mccall_with_sep_markov)=
@@ -22,7 +20,7 @@ jupyter:
 </div>
 ```
 
-
++++
 
 # Job Search III: Search with Separation and Markov Wages
 
@@ -104,6 +102,7 @@ $$
     \right]
 $$
 
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 ## Computational Approach
 
@@ -121,6 +120,7 @@ $$
 
 2. Substitute into the unemployed agent's Bellman equation to get:
 
++++
 
 $$
     v_u(w) = 
@@ -137,6 +137,7 @@ $$
 
 The optimal policy turns out to be a reservation wage strategy: accept all wages above some threshold.
 
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 ## Code
 
@@ -334,6 +335,7 @@ plt.show()
 
 Can you provide an intuitive economic story behind the outcome that you see in this figure?
 
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 ## Employment Simulation
 
@@ -492,7 +494,7 @@ This is because she uses the wage $w$ from her last job to draw a new wage offer
 via $P(w, \cdot)$, and positive correlation means that a high current $w$ is
 often leads a high new draw.
 
-
++++
 
 ## The Ergodic Property
 
@@ -545,6 +547,7 @@ As a result, we can study steady-state unemployment either by:
 
 Often the second approach is better for our purposes, since it's easier to parallelize.
 
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 ## Cross-Sectional Analysis