--top isn't respected in driver.cpp for circt-rtl-sim.py

driver.cpp includes Vtop.h, which assumes the toplevel module is named top. circt-rtl-sim.py takes a parameter to set the toplevel name to something else, but the driver still assumes it's "top".

Start by tracing how circt-rtl-sim.py passes the --top parameter into driver.cpp, then inspect the Vtop.h include and related generated-module assumptions. Done means the simulator uses a non-top toplevel name successfully instead of always requiring a module named top.

Written by the indexing model from the issue text.