fix: refactor types for rsaFunctionFor to include BufferLike

[JonathanYeeW]

Why

This PR updates the returned function parameter types for rsaFunctionFor() to include BufferLike. The original code already performs checks and assumes that EncodingOptions can be a BinaryLike, but this type wasn’t properly reflected in the definitions.

This omission causes issues during TypeScript compilation (tsc) in cases where passing a private key works as intended but fails the type check. For example:

const symmetricKey = crypto.privateDecrypt(
    privateKey,
    Buffer.from(encryptedSymmetricKey, "base64")
  );

Also noting, this change does the type checking logic inline. Normally, I’d pull these into utility functions to keep the function body cleaner and more focused. However, I’m unsure where this type of utility would belong in the project structure. Additionally, given that this functionality might be deprecated, I’m not certain if it’s worth the effort to refactor at this point.

That said, I’m happy to make changes based on the team’s preferences.

What

• Added BufferLike to the function’s returned parameter types.

[boorad]

@JonathanYeeW tyvm ❤️