Can't peek / poke sliced bits in Tester

[ducky64]

Looks like the Tester expects that every node peek'd / poke'd needs to have a corresponding name in the emulator. Naturally, sliced bits of a multibit wire wouldn't actually "exist" in the emulator for access, which fails a check in the Tester and crashes with a completely unhelpful error message.

[sdtwigg]

This is symptomatic of the more general issue that the design is not actually frozen when sent to the tester (after an emulator has been emitted). For example, trying to peek on two IO's added or concatenated together would yield a similar error.