Update Redis Constraint to Reflect Documentation

[matthewshirley]

In PR #67, the Redis constraint was removed (>=5.0,<7.0) and reintroduced for >6.2.0 in 13ddc96. As per the README, redis>=5.2.1 is the minimum version supported.

I don't, as far as I can tell, believe the ^6.2.0 constraint is correct. However, if it is, I can alternatively update the documentation.

[bsbodden]

The redis version constraint change looks good and aligns with the documentation. However, this PR will fail CI due to mypy errors introduced by stricter type hints in redis-py 6.3.0+.

The following files need type casting fixes to pass mypy checks:

---

File: langgraph/checkpoint/redis/shallow.py (around line 641)

Change:

return self._deserialize_channel_values(channel_values)

To:

# Cast to dict[str, Any] as we know this is the correct type from checkpoint structure
from typing import cast

return self._deserialize_channel_values(
    cast(dict[str, Any], channel_values) if channel_values else {}
)

---

File: langgraph/checkpoint/redis/aio.py

Three locations need cast(Any, write_obj):

• Line 1144: await self._redis.json().set(key, "$", cast(Any, write_obj)) # type: ignore[misc]
• Line 1200: pipeline.json().set(key, "$", cast(Any, write_obj))
• Line 1267: fallback_pipeline.json().set(key, "$", cast(Any, write_obj))

---

File: langgraph/checkpoint/redis/__init__.py

Two locations need cast(Any, write_obj):

• Line 604: pipeline.json().set(key, "$", cast(Any, write_obj))
• Line 639: fallback_pipeline.json().set(key, "$", cast(Any, write_obj))

---

Root cause: redis-py 6.3.0+ introduced stricter JsonType type hints for JSONCommands.set() that require explicit casting.

Verification: All 350 tests pass with these changes and mypy passes cleanly.

[bsbodden]

Closing in favor of #103 in order to make into the release. Thank you @matthewshirley