Empty blackbox context for imap_go

[kleinreact]

We got the following error in bittide-hardware (see this CI run):

<no location info>: error:

    Clash.Netlist.BlackBox(218): Couldn't instantiate blackbox for Clash.Sized.Vector.imap_go. Verification procedure reported:

    Blackbox requested instantiation of function at argument 1, but BlackBoxContext did not contain one.

which was introduced by this simple change.

Unfortunately, we were not able to create a smaller reproducer for this in a reasonable amount of time. All our efforts to reconstruct the situation worked out just fine.

Hence, the easiest way to reproducing this bug at the moment is to check out the aforementioned commit, enter the provided nix shell and run shake hwCcTopologyTest:hdl.