Add MSI MD342CQP monitor support

[xizha127]

Add support for the MSI MD342CQP monitor.

Changes:

• Add MD342CQP model identity (s140 = 00 a0, s150 = V20).
• Enable settings verified on hardware: macro_key, frequency, response_time, eye_saver, image_enhancement, brightness, contrast, sharpness, input, osd_transparency, osd_timeout, and kvm.
• Enable the input choices reported by MSI Display Switch for this model: hdmi1, hdmi2, dp, usbc.
• Enable KVM choices: auto, upstream, type_c.
• Allow the libusb backend to match a device when the product filter is empty. This is needed by mondev_t probing with the libusb path.
• Add MODE="0660" to the packaged udev rules so the plugdev group assignment grants access reliably.
• Include <cstdint> in psteelseries.h for uint8_t/uint16_t on current toolchains.

Tested on Linux with an MSI MD342CQP exposed as USB HID controller 1462:3fa4:

$ ./msigd --info
Vendor Id:      0x1462
Product Id:     0x3fa4
Product:        MSI Gaming Controller
Serial:         A02019010700
Monitor Series: MD342CQP
LED support:    None

$ ./msigd -q
macro_key : off
frequency : 060
response_time : fast
eye_saver : off
image_enhancement : off
brightness : 100
contrast : 70
sharpness : 0
input : dp
osd_transparency : 0
osd_timeout : 15
kvm : upstream

Also tested:

• make
• make USE_HIDAPI=0
• ./msigd -q -f input,kvm
• ./msigd --kvm upstream

I did not intentionally switch KVM to type_c during final testing because doing so can move USB control away from the Linux host currently running msigd.