test/programs/maps.flan is seven claims over the Map, each one a
plausible wrong version gets wrong, with the numbers differing per
failure so a single wrong answer names its own cause: an integer key
past eight grows, a struct key whose padding must never be hashed, a
struct key holding a string, an enum key, clone's independence, upsert
not growing the length, and a map living in an arena.
The move refusal said "a Vec is move-only" whatever had been moved, so
moving a Map was reported as a fact about Vecs. It names the type now.
Joseph Ferano
e0aedadd74