[beinan]

Summary

context-wal-lab disk reported raft-engine's segment-size estimate as disk_bytes. Batches can overshoot the target segment size, so that estimate can understate the actual WAL footprint.

Measure the closed engine's regular files outside write/reopen timing, report apparent and allocated sizes, and retain the engine estimate separately. disk_bytes now sums each file's larger apparent/allocated size. These fields measure directory footprint, not physical bytes written or write amplification.

Refs #378.

Testing

• Real raft-engine regression with synced batches larger than the target segment size; added to CI.
• Release lab tests, feature-enabled Clippy, and CLI disk/reopen/full-payload smoke passed.
• Workspace formatting, Clippy and all-target tests passed (603 tests; 154 ignored by default).
• Python: 220 passed, 11 skipped, one expected failure; Ruff and Pyright passed. Installed the declared test/dev extras to complete the helper's Python checks.