fix(checkpoint-postgres): Replace f-string SQL formatting with parameterized queries in migration statements (#6328)

## Summary

Replace f-string SQL formatting with parameterized queries to prevent
potential SQL injection in checkpoint migration code.

## Changes

Updated the migration version tracking INSERT statements in all
checkpoint saver classes to use parameterized queries instead of
f-string formatting:

- `PostgresSaver`
(libs/checkpoint-postgres/langgraph/checkpoint/postgres/__init__.py:100)
- `AsyncPostgresSaver`
(libs/checkpoint-postgres/langgraph/checkpoint/postgres/aio.py:104-106)
- `ShallowPostgresSaver`
(libs/checkpoint-postgres/langgraph/checkpoint/postgres/shallow.py:255)
- `AsyncShallowPostgresSaver`
(libs/checkpoint-postgres/langgraph/checkpoint/postgres/shallow.py:617-619)

**Before (vulnerable to SQL injection):**
```python
cur.execute(f"INSERT INTO checkpoint_migrations (v) VALUES ({v})")
```

**After (using parameterized query):**
```python
cur.execute("INSERT INTO checkpoint_migrations (v) VALUES (%s)", (v,))
```

## Risk Assessment

The practical risk is low since `v` is an integer loop variable
controlled by the codebase. However, using string formatting in SQL
queries is a well-known anti-pattern that can lead to SQL injection
vulnerabilities, especially if the code is later refactored or copied to
other contexts.

## Testing

- ✅ All 216 tests passing on PostgreSQL 15 and 16
- ✅ Linting and type checking passing
- ✅ No functional changes to behavior

libs/checkpoint-postgres/langgraph/checkpoint/postgres/__init__.py

@@ -97,7 +97,7 @@ class PostgresSaver(BasePostgresSaver):
                 strict=False,
             ):
                 cur.execute(migration)
-                cur.execute(f"INSERT INTO checkpoint_migrations (v) VALUES ({v})")
+                cur.execute("INSERT INTO checkpoint_migrations (v) VALUES (%s)", (v,))
         if self.pipe:
             self.pipe.sync()
 

libs/checkpoint-postgres/langgraph/checkpoint/postgres/aio.py

@@ -102,7 +102,9 @@ class AsyncPostgresSaver(BasePostgresSaver):
                 strict=False,
             ):
                 await cur.execute(migration)
-                await cur.execute(f"INSERT INTO checkpoint_migrations (v) VALUES ({v})")
+                await cur.execute(
+                    "INSERT INTO checkpoint_migrations (v) VALUES (%s)", (v,)
+                )
         if self.pipe:
             await self.pipe.sync()
 

libs/checkpoint-postgres/langgraph/checkpoint/postgres/shallow.py

@@ -252,7 +252,7 @@ class ShallowPostgresSaver(BasePostgresSaver):
                 strict=False,
             ):
                 cur.execute(migration)
-                cur.execute(f"INSERT INTO checkpoint_migrations (v) VALUES ({v})")
+                cur.execute("INSERT INTO checkpoint_migrations (v) VALUES (%s)", (v,))
         if self.pipe:
             self.pipe.sync()
 
@@ -614,7 +614,9 @@ class AsyncShallowPostgresSaver(BasePostgresSaver):
                 strict=False,
             ):
                 await cur.execute(migration)
-                await cur.execute(f"INSERT INTO checkpoint_migrations (v) VALUES ({v})")
+                await cur.execute(
+                    "INSERT INTO checkpoint_migrations (v) VALUES (%s)", (v,)
+                )
         if self.pipe:
             await self.pipe.sync()