refactor: polish handling of HttpQuery waiting for final.

[youngsofun]

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Summary

User may not call conn.close(), to avoid meaningless timeout check and heartbeat.
we can mark the query as Finished after the last page has returned for 30s and stop them.
because client retry should not take as long as result_timeout_secs.
heartbeat_handler should notify client that no need for heartbeat anymore.

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):

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This change is