fix(node): exclude internal events from public union

[hogeheer499-commits]

Summary

Fix the Node SDK's generated public SessionEvent declaration after internal event wrappers are stripped from the published package.

The generator already excluded variants whose data schema is internal, but assistant.turn_retry and model.call_start mark the event wrapper itself as internal. Their interfaces were removed by stripInternal, while their names remained in the public union. This left the published declaration with unresolved references and caused event payload types to degrade for consumers using skipLibCheck.

This change filters variants when either the resolved wrapper or its data schema is internal, regenerates the TypeScript session events, and adds a regression test for the wrapper-internal/data-public case.

Fixes #2078.

Validation

• npx vitest run test/*.test.ts — 243 tests passed
• npm run build
• npm run typecheck
• npm run lint — no errors (3 existing warnings)
• npm run format:check
• Compiled dist/generated/session-events.d.ts with skipLibCheck: false
• git diff --check