test(systest): add query-073 covering reverse counts for all 592 non-empty genres

A comprehensive `count(~genre)` check across every Genre entity in
the 21million dataset. The query asks for each genre's name and the
size of its reverse posting list, sorted by name; the fixture pins
the expected count for all 592 genres that have at least one film.

Motivation: the per-predicate mutation pipeline had a buffer-aliasing
bug (fixed in 0a9ffc1) that produced wrong reverse-list contents
on a different small subset of genres each load — sometimes
Documentary lost most of its 31,370 entries, sometimes
Children's/Family gained ~1,500 spurious Crime-Thriller entries,
sometimes Backstage Musical and Indie film were the affected pair.
The existing query-017 (Taraji-films-by-genre) only catches it when
that specific actor's films happen to land on a corrupted genre,
and query-016 / query-044 only test genres above 30,000 films.

This new query exercises every genre's reverse list and pins the
exact expected count, so any regression that mis-routes reverse
edges for any genre will fail it directly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: matthewmcneely