Handle prepared-statement placeholders in plan monitor

[wayyoungboy]

Summary

• make prepared-statement parameter filling skip ? inside strings, quoted identifiers, and comments
• skip EXPLAIN extended when SQL audit text still contains unfilled parameter placeholders
• add unit coverage for PS placeholder replacement and plan monitor EXPLAIN eligibility

Fixes #420

Verification

• PYTHONPATH=. python -m pytest test/common/test_fill_sql_with_params.py test/gather/test_gather_plan_monitor_ps_sql.py test/common/test_scene.py -q
• black --check -S -l 256 src/common/tool.py src/handler/gather/gather_plan_monitor.py test/common/test_fill_sql_with_params.py test/gather/test_gather_plan_monitor_ps_sql.py
• python workflow_data/check_py_files.py .
• git diff --check