Replace cnfast with cn
Internal refactor only.
Bundle TypeScript for Twoslash
fumadocs-twoslash now depends on its own TypeScript 6 and passes it to Twoslash, so the transformer keeps working in projects on TypeScript 7 (whose package no longer provides the compiler API Twoslash requires). Previously, every Twoslash code block that was not already in the types cache failed with Cannot read properties of undefined (reading 'readFile').