v2.203.0 — E151: verify_roundtrip fits a source offset from the majority

Fixed

• verify_roundtrip fits a source's offset from the majority of its
  cuts. The per-source timecode offset was whatever the FIRST paired cut
  said, so on a real reel two shifted cuts of fifty-five set the expectation
  and fifty-three unchanged cuts read as source-frames drift. The offset is
  now the source's dominant one across all its pairs (net of record shift),
  and each cut is judged against that. On that reel: 137 → 76 mismatches,
  the remainder the per-cut scatter of an eye-matched re-conform; the other
  reels lose two false drifts each.