perf(ext/web): align queue retain capacity with node reference
Resolves the tune-constants TODO from the refinement handoff. Cribs the
values from nodejs/node#64312, which uses the same ring buffer for the
same spec structure: initial capacity 8 (already matched) and a retain
threshold of 1024 entries (was 512). The larger threshold keeps a ring
that grew during a burst reusable across full drains (e.g. the buffered
read n=1000 shape), while still dropping rings above the threshold when
the queue empties so a one-off spike does not pin a large backing array.
Comments updated to cite the upstream reference.
