* fix(scrub): don't flag offset-0 logical tombstones in volume scrub
A remote-tier delete records a tombstone at .idx offset 0 with no physical .dat
bytes. Full scrub double-flagged a healthy remote-tiered volume with deletes:
scrubVolumeData counted the tombstone's GetActualSize(-1)=32 toward totalRead
(want > physical .dat), and CheckIndexFile treated it as occupying [0,31] and
flagged the first live needle as overlapping. Skip offset-0 logical tombstones
from both the size reconcile and the overlap check; they are still counted for
the index-size check. Local deletes (offset != 0) are unaffected.
Claude-Session: https://claude.ai/code/session_015EE9Sc9EvNp8BCVva4RKdo
* fix(scrub): mirror offset-0 logical tombstone handling into Rust
Same fix as the Go volume_checking.go + idx/check.go change: Volume::scrub skips
offset-0 logical tombstones from total_read, and check_index_file excludes them
from the overlap check (still counted for the index-size check).
Claude-Session: https://claude.ai/code/session_015EE9Sc9EvNp8BCVva4RKdo
Implement index (fast) scrubbing for regular/EC volumes via `ScrubVolume()`/`ScrubEcVolume()`.
Also rearranges existing index test files for reuse across unit tests for different modules.
Chris Lu