Generate CJS version of otpauth.d.ts file

[wpf500]

I use your library in a TypeScript project and have just been updating my build. When I changed my TSConfig option module from commonjs to node16 I started getting the following error when importing your library:

import { TOTP } from "otpauth";
// The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'. Consider writing a dynamic 'import("otpauth")' call instead.
//  To convert this file to an ECMAScript module, change its file extension to '.mts' or create a local package.json file

After a lot of digging it turns out this is because while your library does specify an export for Node CommonJS libraries (
https://github.com/hectorm/otpauth/blob/master/package.json#L44), it doesn't specify a CommonJS type definition file. TypeScript assumes that because the type definition file ends d.ts rather than d.cts the package is an ESM package and fails (more info here: microsoft/TypeScript#53045)

This PR adds the relevant lines that tells TypeScript that it can treat this as a CommonJS library. Note moving types down in exports is necessary because otherwise it matches the first types before getting to the Node CommonJS specific one.

[hectorm]

Thanks for your contribution! I don't usually work with TypeScript, but I've reviewed your changes and although they look good, I think they could be improved with the suggested changes.

[wpf500]

@hectorm I think I've addressed all your comments now

[hectorm]

LGTM, thanks!