feat(bindings): expose parentEventId on Event

[cesarenaldi]

Summary

The wire schema already parsed parentEventId but normalizeEvent dropped it, so the public Event never exposed it. Sports "more markets" events carry this field as a link to their parent game event.

• Event.parentEventId?: EventId | null, top-level next to id.
• Wire value arrives as an integer while event ids are strings; it now goes through EventIdSchema so the value is the same branded EventId type as Event.id and feeds directly into fetchEvent({ id: child.parentEventId }).
• Mirrors py-sdk PR feat(models): add parent_event_id to Event py-sdk#96 (same gap reported in [Feature]: add parentEventId to Event py-sdk#93).

Not in scope: the listEvents parentEventId request filter still only accepts a number, same as the other ID filters (ids, seriesIds). Aligning the filter inputs with branded string IDs is a broader consistency change worth a separate pass.

Verification

• pnpm lint, pnpm build, pnpm typecheck pass.
• pnpm test:types, pnpm test:bindings (15), pnpm test:client (123) pass.
• New bindings tests cover int-to-EventId normalization and absent/null defaults (the regression here was the normalizer silently dropping the field).
• Live smoke against the built client: fetchEvent({ id: '570555' }) returns parentEventId === '570146', round-trips via fetchEvent({ id: child.parentEventId }), and the parent's own parentEventId is undefined.

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Note

Low Risk
Additive, read-only API surface on event parsing with targeted tests; no auth or write-path changes.

Overview
Exposes parentEventId on the public Event type so child events (e.g. sports “more markets”) can reference their parent. The Gamma wire field was already parsed but normalizeEvent now forwards it instead of dropping it.

parentEventId is typed and parsed as EventId, matching Event.id: wire integers are normalized to string IDs via EventIdSchema (replacing a raw number on the schema). New bindings tests cover int→string normalization and absent/null handling.

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