[FEAT]: Replace `standalone` config option flag with new option to specify visa backend

[nfelt14]

Description

The current standalone option can be a little confusing since the option name doesn't make it clear it affects the VISA backend. It would be nice if a new option was created that allowed the user to specify any string indicating a VISA backend that they would like to use.

Additional Information

No response

[nfelt14]

The first release should simply deprecate the standalone option (leave it in and working, but raise a DeprecationWarning) and then when v4.0 is released, it can be removed.