LangGraph: Namespace labels containing `.` reach other namespaces in Postgres and SQLite stores

LangGraph checkpoint savers provide Postgres- and SQLite-backed state persistence for LangGraph workflows and agents. Prior to langgraph-checkpoint-postgres 3.1.3 and langgraph-checkpoint-sqlite 3.1.2, PostgresStore, AsyncPostgresStore, SqliteStore, and AsyncSqliteStore flatten namespace labels with ".".join(namespace), while BaseStore validates labels only for put and aput. Unvalidated dotted labels passed through get, search, delete, list_namespaces, their asynchronous equivalents, or direct batch and abatch operations can resolve to another tenant's stored namespace, allowing cross-namespace reads, overwrites, or deletion. InMemoryStore is not affected because it compares namespace tuples. This issue is fixed in langgraph-checkpoint-postgres 3.1.3 and langgraph-checkpoint-sqlite 3.1.2.