Make USB communication work again (with my Mac and Oscilloscope, at least)

[th-in-gs]

• (On some platforms?) pyvisa-py uses decimal numbers for the VID/PID values. This change allows both the hex and decimal representations to work when finding the Rigol device.
• After fixing the above, I could still never get a screenshot to save - there were always errors deep in pyvisa. The problem I was having is documented here: https://github.com/pyvisa/pyvisa/issues/481. '64 - 12' (52) seems to be the maximum chunk size that allows reliable communication. I left it as '64 - 12' in this change rather than simply 52 to match the code quoted in that issue.

Both these changes were required to allow the script to work with my scope (a MSO1075Z), running DS1000Z firmware v00.04.05.02.00, connected to my M2 Mac running macOS Ventura 13.3.1.