This PR should be the base for discussion, do not merge it yet!
It correctly detects reg/wire mix and incorrect use on blocking,nonblocking assignments within blocks and assign statements.
What it DOES'T do:
Detect registers connected to output ports of instances.
Where it FAILS:
memorty nonblocking assignments causes spurious (I assume??) errors on yosys-generated "_ADDR", "_DATA", "EN" signals.
You can test it with tests/simple/reg_wire_error.v (look inside for the comments to enable/disable specific lines)