Implement USB TMC

[MatzeS]

In addition to network communication the USB interface should be implemented.
I assume this is a fairly straight forward task, to send the existing commands over a different communication interface - USB TMC instead of network.

Apparently there are some crates to implement USB TMC:

• https://crates.io/crates/tmc
• https://crates.io/crates/rs-usbtmc
• https://crates.io/crates/usbtmc

Should it become necessary, here the USB TMC Spec: https://www.usb.org/document-library/test-measurement-class-specification

[MatzeS]

Debugging documentation:
The rs-usbtmc appears to be working when sending some basic command strings.
However, on for one of our devices there are issues with the *IDN? command.
The complete response would be "Siglent Technologies,SPD3303X,SPD3XJGQ805993,1.01.01.03.11R1" which exceeds the 64 byte transfer size on the REQUEST_DEV_DEP_MSG_IN message.
Either the rs-usbtmc crate or the SPD3303X USB driver implementation apparently have a bug that causes issues splitting the payload over multiple messages.
A quick workaround is to increase the TransferSize in the REQUEST_DEV_DEP_MSG_IN to a sufficiently large value, which avoids message fragmentation. However, I am currently not sure if this would be according to USB specification.