daqmx: investigate OneShot mode

When working on #8107 and #6049 initially `OneShot` mode was tried. This didn't seem to work, record scanned but never got a value. The included example used `OneShot N=1 F=0` however the hardware did not accept `N=1` and so `OneShot N=2 F=0` was used which didn't work. The problem may be using `N=2` and the OneShot mode is normally fine, a brief look at the code couldn't see why `N=2` may be an issue, but this needs to be checked.

## Acceptance Criteria

Behaviour of `OneShot` mode checked and documentation/code fixes applied as necessary