The files table gets a disk_size column: the file's allocated blocks,
st_blocks × 512, from the lstat the walk already does. scan writes it
with every record it writes. When a rescan finds a file with its size
and mtime unchanged but a different disk_size, it updates disk_size
alone, without reading the file. trees adds disk_size up per directory
and prints it as a column after size. On a compressed or sparse file it
is less than size, so two copies of one tree can differ; each row shows
the dupe copy's.
Judgement calls: a row's disk_size is the dupe copy's, not the first's.
A file whose record gets only a new disk_size counts as unchanged.
Model: opus-5-5
sneak