Point package.json "types" field to generated .d.ts instead of raw .ts

[kkelk]

The current config results in the dependent package compiling this package, which works in most cases but can fail if the dependent package has an incompatible tsconfig.json, e.g. by applying stricter options such as exactOptionalPropertyTypes.

This PR should bring the package in-line with the standard way of doing this, making sure it works for all tsconfig.json settings. It looks like a similar change was already made in the main elysia package as part of this commit.