A deep oneOf chain joined the accumulated union string at every level
(Array.join forces materialization), making it Theta(depth^2) — a
50,000-level chain took ~7.6s. Concatenate with `+` instead: V8 builds a
lazy ConsString that materializes once at the root, matching the array
arm's template-literal laziness and ts-types' composable-document approach.
The whole walk is now linear in depth. Adds a 20,000-level oneOf test
alongside the existing deep-array one; py-types.ts stays at 100% coverage.
Chinesezjc
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