The server stores only nest-level metadata, so a browser that shows a
saved nest's plates and drawings has to read them from its archive.
NestDetails.FromNest turns a nest into one row per plate (duplicates,
size, parts and distinct drawings without cutoffs, utilization; 0 for a
zero-size plate rather than NaN) and one row per non-cutoff drawing
(required, nested across every plate's duplicates, remaining, area),
plus the nest's units.
NestDetailsSession loads the details of the highlighted nest. A new
load or Clear supersedes the previous one before cancelling it, so a
load that completes synchronously on cancellation and any late result
or failure of a superseded load are discarded; IsLoading follows only
the latest load.