Add soft-connection check

Add a soft-connection check to CACE as a tool.

It checks whether the netlist extracted from the layout matches the netlist extracted from the layout without well/substrate connections. CACE will need to generate a custom magic tech file.

Start by tracing CACE's existing netlist extraction and tool checks, then identify where a custom Magic tech file would be generated. Done means CACE compares the layout netlist with the netlist extracted without well/substrate connections and exposes the soft-connection check as a tool.

Written by the indexing model from the issue text.