chore: Upgrade TypeScript from 4.9.5 to 5.x

[antonis]

Summary

Upgrade the build-time TypeScript version from 4.9.5 to 5.x (targeting ~5.8 to align with sentry-javascript).

Motivation

• Enable type-aware oxlint linting — After migrating to oxlint (RN-479 / chore: Migrate from ESLint to oxlint #5867), type-aware rules like no-floating-promises, unbound-method, and no-unsafe-member-access are configured but not enforced at runtime. Enabling --type-aware requires oxlint-tsgolint, which needs TypeScript 5.x+. With TS 4.9.5, the DANGEROUSLY_SUPPRESS_PROGRAM_DIAGNOSTICS workaround produces too many false positives.
• Align with ecosystem — sentry-javascript uses TS ~5.8, React Native 0.80 ships with TS 5.0.4, Expo 55 uses TS ~5.9. The RN ecosystem is solidly on TS 5.x.
• TS 4.9 is unmaintained — Released in Nov 2022, no longer receives patches.

Not a breaking change

The TypeScript version is a build-time devDependency. The emitted .d.ts types are downleveled to TS 3.8 via downlevel-dts, so users can consume the SDK with any TypeScript version >= 3.8. This does not require a major version bump.

Scope

1. Bump typescript from 4.9.5 to ~5.8.0 in packages/core/package.json
2. Fix any new type errors surfaced by TS 5.x (stricter checks)
3. Add oxlint-tsgolint and enable --type-aware flag in lint scripts
4. Verify downlevel-dts still produces valid TS 3.8 types (CI already checks this)

Related

• chore: Migrate from ESLint to oxlint #5867 — Migrate from ESLint to oxlint
• RN-479 — Investigate migrating from ESLint to oxlint

[linear-code]

RN-549