1.0.0rc1

Changes since 0.6.10

• chore: release rcs for prebuilt + langgraph (#6296)
• chore: drop Python 3.9 (and syntax) (#6289)
• docs: style linting (#6260)
• release(langgraph): v1 working branch (#6093)
• fix: rename away from LangGraph Platform (#6281)