Update transfer-ID handling

[pavel-kirienko]

See https://forum.opencyphal.org/t/improve-the-transfer-id-timeout/2375

We don't maintain the transfer-ID counters internally in the library during transmission, so it is up to the application to come up with randomness.

The TRANSFER_ID_UNSET will need to be replaced with a new state:

https://github.com/OpenCyphal/libudpard/blob/3d9f5efc26b91d7c9bf9104f55551ea7ad454dc2/libudpard/udpard.c#L41C9-L41C26

The RX pipeline will need to be extended with the one-million difference check.