ludic.things: a removed Thing's record placed again, oldest first past a lag of 32; things_reserve sizes the grid once

thing_put and thing_spawn made a new record for every Thing placed, and the world places and removes
them all day (an animal's sign and bed, a drop, a fish), so play grew by a record per placement.
Removed records wait in a queue compacted in place; once 32 wait, the oldest is set back as new
with a new uid. ludic.base's grid_reserve makes the buckets for n rows now, since a rehash in play
leaves the old bucket array behind. Tests: a record comes back only past the lag, as new, with a
new uid, the indexes agree, and the spare queue stays bounded.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.base/ecs_grid_file.ludic

@@ -38,3 +38,9 @@ function grid_rehash(g: Grid) -> void {
     if k >= 0 { grid_link(g, r, k, grid_bucket(g, grid_key_x(k), grid_key_z(k))) }
   }
 }
+
+# buckets enough for `rows` filed rows before a rehash, made now: a rehash in play makes a new
+# bucket array and nothing gives the old one back
+export function grid_reserve(g: Grid, rows: int) -> void {
+  while (g.mask + 1) * 2 < rows { grid_rehash(g) }
+}