Request: Add partitions

[xdsopl]

The limit of 1024 blocks is an artificial one, in order to avoid excessive time needed for decoding:

Data for the plot was created on a Raspberry Pi 400, which has an 1.8GHz ARM Cortex-A72.

To work around the limit, we could split larger files into partitions.
We even have enough bits in the current header for that:

• 2 bits: 1, 2, 4 and 8 partitions
• 3 bits: partition number 0 .. 7

So 5 bits from 6 available from the number of splits field could be used to increase the file size eight fold with the same number of blocks.

Another nice bonus would be to have the possibility to preview one of the successfully decoded partitions:
If we send the first partition more often than the other ones, we could see the beginning of the file first, before the transmission is even complete.