docs: add comprehensive migration guide for 0.2.0 and remove Python 3.9 from CI

- Add MIGRATION_0.2.0.md with detailed migration instructions for:
  * LangGraph 1.0 Interrupt API changes (4 fields → 2 fields)
  * Checkpoint 3.0 serialization changes (str → bytes)
  * Python 3.10+ requirement
  * Data migration strategies and troubleshooting
- Rename MIGRATION.md to MIGRATION_0.1.0.md for version clarity
- Remove Python 3.9 from CI test matrix (EOL and no longer supported)

The migration guide covers:
- Breaking changes with before/after code examples
- Step-by-step migration process
- Data compatibility and migration options
- Comprehensive troubleshooting section
- Testing recommendations

Author: bsbodden

.github/workflows/test.yml

@@ -24,7 +24,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [ 3.9, '3.10', 3.11, 3.12, 3.13 ]
+        python-version: [ '3.10', 3.11, 3.12, 3.13 ]
         redis-version: [ '6.2.6-v9', 'latest', '8.0.2' ]
 
     steps:

MIGRATION.md renamed to MIGRATION_0.1.0.md

@@ -24,14 +24,16 @@ This library is currently at version 0.1.0. As the library evolves, the followin
 The library uses structured Redis key patterns:
 
 **Standard RedisSaver (full history):**
-```
+
+```txt
 checkpoint:{thread_id}:{checkpoint_ns}:{checkpoint_id}
 checkpoint_blob:{thread_id}:{checkpoint_ns}:{channel}:{version}
 checkpoint_write:{thread_id}:{checkpoint_ns}:{checkpoint_id}:{task_id}:{idx}
 ```
 
 **ShallowRedisSaver (latest only):**
-```
+
+```txt
 checkpoint:{thread_id}:{checkpoint_ns}  # Single checkpoint per thread/namespace
 ```
 
@@ -88,10 +90,12 @@ saver = RedisSaver(
 ## Redis Module Requirements
 
 ### Redis 8.0+
+
 - Includes RedisJSON and RediSearch modules by default
 - Recommended for production use
 
 ### Redis < 8.0
+
 - Requires Redis Stack or manual installation of:
   - RedisJSON module
   - RediSearch module
@@ -109,4 +113,4 @@ If you encounter issues during migration:
 
 1. Check the [GitHub Issues](https://github.com/redis-developer/langgraph-redis/issues) for known problems
 2. Review the [Release Notes](https://github.com/redis-developer/langgraph-redis/releases) for version changes
-3. Open a new issue with details about your migration scenario
+3. Open a new issue with details about your migration scenario