fix: dynamically require typescript

[paescuj]

Fixes #798

Dynamically load typescript via require, so that it only needs to be installed on user-side when type checking is enabled.
Tested in ESM and CJS context ✅

Notes:

• This issue hasn't really surfaced as pnpm (and possibly other package managers) automatically installs peer dependencies.
• We need to rely on require instead of dynamic import because ESLint rules can't be async.
• As an alternative, we could declare typescript as a prod dependency ourselves or bundle it. However, since typescript is necessary on user-side for type checking anyway, this seems to be the most appropriate solution.