Add Qdrant-backed checkpoint saver and memory store (langgraph-checkpoint-qdrant)

Hi,

I’d like to contribute a new library libs/checkpoint-qdrant/ that adds
Qdrant as a backend for both the LangGraph checkpoint saver and the
long-term memory store.

Motivation: Qdrant is widely used in LangGraph-based apps for vector
search. Users who already run Qdrant in their stack currently have to
introduce a second database (Postgres or SQLite) just for checkpointing.
Having a native Qdrant implementation removes that friction.

Proposed API:

  • QdrantSaver / AsyncQdrantSaver — checkpoint saver
    (langgraph.checkpoint.qdrant)
  • QdrantStore / AsyncQdrantStore — memory store with optional vector
    similarity search, namespace filtering, and TTL
    (langgraph.store.qdrant)

The implementation follows the same structure and semantics as
checkpoint-postgres and checkpoint-sqlite. I have a working
implementation ready with 40 tests passing (ruff + mypy clean, tested
against both in-memory and real Docker Qdrant).

Happy to open a PR as soon as this is approved. Let me know if you’d
like me to adjust anything in the API design.

Current implementation here: GitHub - gianlucaperna/langgraph at feat/checkpoint-qdrant · GitHub

Thanks!