checkpoint==2.1.0

Changes since checkpoint==2.0.26

• langgraph-checkpoint 2.1.0
• Preparation for 0.5 release: langgraph-checkpoint (#5124)
• Restore compatibility with custom checkpointer classes created in prior versions
• serialize/deserialize pandas with pickle fallback (#5057)
• Support numpy array serialization in JsonPlusSerializer (#5035)
• Update ormsgpack (#5034)
• lint: use pep 604 union syntax and pep 585 generic syntax (#4963)
• Remove Checkpoint.writes
• Remove Checkpoint.pending_sends
• ci: migrate to uv! (#4698)