Export Engines/KeyStores through `@token-io/tpp`

[bkniffler]

I'd like to implement a custom KeyStore / CryptoEngine like:

export class CryptoEngine extends KeyStoreCryptoEngine {
  constructor(memberId: string) {
    super(memberId, myCustomkeyStore);
  }
}

But KeyStoreCryptoEngine is not exported by @token-io/tpp neither is any other except for the filesystem one (inside of TokenClient). I know it is exported from @token-io/core but since it uses esmodules and flow, I can't use it from my nodejs without transpiling.