RE pull resistors:

Currently, the benchmark applet is broken. Running it gives the following output:
```
samuelz@sz-t14 ~/D/g/g/software (main) [2]> glasgow run benchmark
I: g.hardware.device: generating bitstream ID 659ea3484cb48ddd76737b5e77b987dd
I: g.cli: running handler for applet 'benchmark'
E: g.cli: cannot set I/O port(s) AB pull resistors to low={} high={}
```

The benchmark applet doesn't enable the I/O voltages, and also hides the voltage argument. This causes it to fail when `DeprecatedDemultiplexer` tries to set the pulls.

As a solution, would it make sense to not try and set pulls for I/O banks set to 0V?

Also, the `-V`/`--voltage` argument is not required anymore which means that forgetting it gives the same error which is confusing. (See below)
```
samuelz@sz-t14 ~/D/g/g/software (main) [1]> glasgow run uart
I: g.hardware.device: generating bitstream ID ebcb64c1185836f8f9b36fac83902c8f
I: g.cli: running handler for applet 'uart'
E: g.cli: cannot set I/O port(s) AB pull resistors to low={} high={0}
```