LangGraph: namespace labels containing dots can access other namespaces in Postgres and SQLite storage

LangGraph's langgraph-checkpoint-postgres versions before 3.1.3 and langgraph-checkpoint-sqlite versions before 3.1.2 have a namespace privilege issue: labels containing dots can be used to read, overwrite or delete data in other namespaces. Postgres and SQLite storage join namespace labels with dots, so ("tenant.bob",) and ("tenant", "bob") point to the same storage location, while originally only put validated labels; get, search, delete, list_namespaces and operations passed directly to batch/abatch do not validate. If an application relies on namespaces to isolate users or tenants and lets untrusted input determine labels, data of other tenants may be affected; InMemoryStore compares by tuple and is not affected.