Limit the exports

[jean-michelet]

For now, everything from these folders is exported:

export * from "./providers";
export * from "./modules";
export * from "./hooks";
export * from "./controllers";
export * from "./fastify";

This is convenient, but it also likely exposes internal functions that the library user is not supposed to see.

In each of these folders, there is an index.ts, we should limit the exports to public types and utilities.

The export file: https://github.com/stratifyjs/core/blob/main/src/index.ts