Add Windows LXI/VXI-11 support using VISA

[billboy111]

Summary

Adds native Windows LXI/VXI-11 support to SCPILxiTransport using VISA while retaining the existing liblxi implementation on Linux.

Also enables the LXI transport for the Rigol DHO1000 series.

Windows implementation

• Detects a 64-bit VISA installation with CMake, using VXIPNPPATH64 when available and the standard IVI Foundation VISA path as a fallback.
• Uses viOpenDefaultRM and viOpen to open TCPIP0::::inst0::INSTR resources.
• Uses viWrite and viRead for SCPI communication.
• Existing liblxi behavior on Linux is left intact.

Hardware testing

Built natively on Windows 11 using MSYS2 UCRT64 and tested with a Rigol HDO1074/DHO1074 at 192.168.1.34 using NI-VISA.

Verified:

• Instrument identification over VXI-11/LXI
• Successful ngscopeclient connection using the lxi transport
• Live waveform acquisition
• 1,000,000-point waveform transfers
• Sample-rate and memory-depth changes
• Channel voltage range and offset changes

The same instrument does not respond to raw SCPI over TCP port 5555, while its VXI-11 VISA resource works correctly. This was the reason for adding the existing LXI transport as an option for the DHO1000 series.