File uploading support

[so-saf]

I looked through the CUPS Implementation of IPP documentation and found a few comments:

https://opensource.apple.com/source/cups/cups-218/cups/doc/help/spec-ipp.html#PRINT_JOB

Print-Job Request
...
The Print-Job request is followed by a file to be printed.

https://opensource.apple.com/source/cups/cups-218/cups/doc/help/spec-ipp.html#CUPS_ADD_MODIFY_PRINTER

CUPS-Add-Modify-Printer Request
...
The CUPS-Add-Modify-Printer request can optionally be followed by a PPD file or System V interface script to be used for the printer. ...

So I added the following two lines to the end of the encode_dict function:

if isinstance(data.get("file"), bytes):
    encoded += data["file"]

I've checked printing files and adding printers with a driver on my CUPS server - everything works as expected!

I checked printing files and adding printers with a driver on my CUPS server - everything works as expected!

Furthermore, I know that similar functionality was added in one of the recent PRs, but in addition to changing the encode_dict function, I added another test case and several examples.

And, of course, thanks for the project! Waiting for your reply.