Not a CPC emulator as such, but it's a Z80 simulator that works on the (reverse engineered) Z80 silicon netlist / schematic level - like visual 6502 to some extent.
https://baltazarstudios.com/z80explorer/ (https://baltazarstudios.com/z80explorer/)
Maybe it will be of interest to emulator programmers who want to really know what that bit of silicon is up to!