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Summary

1. better naming
   • HttpQueryState -> ClientState, distingush with execute_state
   • use word closed client to distinguish from stopped execution, and removed from manager
2. clearer state machine
   • remove tombstone by timeout instead of using a fix-sized FIFO queue. and finalized query is removed earlier.
   • Removed confusing is_data_drained atomic bool
3. Data Drainage Tracking
   • Prevents unnecessary timestamp updates after drainage
   • Notifies heartbeat handler when heartbeats are no longer needed

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

This change is