Use sqlite3's online backup API when preserving benchmark snapshots instead of copying .db files directly. This keeps WAL-mode databases consistent for canonical graph comparisons and removes stale destination sidecars before writing the snapshot.
Validation:
- git diff --check
- uv run python -m py_compile scripts/benchmark-incremental-speed.py
Signed-off-by: Andrew Hundt <ATHundt@gmail.com>