Integrate with `iroh`

Here is the example of how to use `iroh`: https://github.com/n0-computer/sendme

It is exactly the same use-case we are solving in Drop ⏤ sending a file by a public key. Iroh takes care of all NAT traversal and data transmission. We only need to prepare QR code with the data necessary to initialize the transfer. Probably, besides the public key also the file checksum should be encoded into the QR.