Update implementation plan with completed phases

- Marked phases 1-7 as completed
- Phase 8 (testing) marked as in progress
- Phases 9-11 pending

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

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

Author: twiecki

IMPLEMENTATION_PLAN.md

@@ -10,16 +10,16 @@ This document provides step-by-step implementation instructions for migrating ho
 
 ## Pre-Migration Checklist
 
-- [ ] Create a new git branch: `git checkout -b pymc5-migration`
-- [ ] Backup current environment configuration
-- [ ] Document current test results baseline: `pixi run pytest homepy/tests/ --tb=short > test_baseline.txt`
+- [x] Create a new git branch: `git checkout -b pymc5-migration`
+- [x] Backup current environment configuration
+- [x] Document current test results baseline: `pixi run pytest homepy/tests/ --tb=short > test_baseline.txt`
 - [ ] Review breaking changes in PyMC v5 release notes
 
 ---
 
-## Phase 1: Environment & Dependency Updates (30-60 min)
+## Phase 1: Environment & Dependency Updates (30-60 min) ✅ COMPLETED
 
-### Step 1.1: Update pyproject.toml
+### Step 1.1: Update pyproject.toml ✅
 
 **File:** `pyproject.toml`
 
@@ -57,9 +57,9 @@ pixi run python -c "import arviz; print(f'ArviZ version: {arviz.__version__}')"
 
 ---
 
-## Phase 2: Global Import Replacements (60-90 min)
+## Phase 2: Global Import Replacements (60-90 min) ✅ COMPLETED
 
-### Step 2.1: Aesara → PyTensor Import Replacements
+### Step 2.1: Aesara → PyTensor Import Replacements ✅
 
 **Files Affected:** All 33 Python files
 
@@ -125,9 +125,9 @@ grep -r "from aesara" homepy/
 
 ---
 
-## Phase 3: AePPL Integration Updates (15-30 min)
+## Phase 3: AePPL Integration Updates (15-30 min) ✅ COMPLETED
 
-### Step 3.1: Update aesaraf.py
+### Step 3.1: Update aesaraf.py ✅
 
 **File:** `homepy/aesaraf.py`
 
@@ -162,9 +162,9 @@ pixi run python -c "from homepy.aesaraf import *"
 
 ---
 
-## Phase 4: Variable Naming Updates (30-45 min)
+## Phase 4: Variable Naming Updates (30-45 min) ✅ COMPLETED
 
-### Step 4.1: Rename `at` variables to `pt`
+### Step 4.1: Rename `at` variables to `pt` ✅
 
 **Files with heavy `at.` usage:**
 - `homepy/models/base.py`
@@ -189,9 +189,9 @@ find homepy -name "*.bak" -delete
 
 ---
 
-## Phase 5: Sampling API Updates (30-45 min)
+## Phase 5: Sampling API Updates (30-45 min) ✅ COMPLETED
 
-### Step 5.1: Update models/base.py sampling calls
+### Step 5.1: Update models/base.py sampling calls ✅
 
 **File:** `homepy/models/base.py`
 
@@ -250,7 +250,7 @@ grep -n "return_inferencedata" homepy/
 
 ---
 
-## Phase 6: Graph Operations Updates (45-60 min)
+## Phase 6: Graph Operations Updates (45-60 min) ✅ COMPLETED
 
 ### Step 6.1: Update aesara.function() calls
 
@@ -293,7 +293,7 @@ from pytensor.graph.rewriting.basic import in2out, node_rewriter
 
 ---
 
-## Phase 7: Random Variable Updates (30-45 min)
+## Phase 7: Random Variable Updates (30-45 min) ✅ COMPLETED
 
 ### Step 7.1: Update RandomStateSharedVariable
 
@@ -325,7 +325,7 @@ shared_var = pytensor.shared(value)
 
 ---
 
-## Phase 8: Testing & Validation (3-6 hours)
+## Phase 8: Testing & Validation (3-6 hours) 🔄 IN PROGRESS
 
 ### Step 8.1: Unit Tests