Which debugger setup do you guys use?

[nm-remarkable]

Have you tried using the LLDB fork? I think that one shows slices correctly

Zig Debugging with LLDB

This is a bit advanced but Jacob Young has a fork of LLDB that adds quite sophisticated Zig support including standard library integration, which is meant to pair with the self-hosted x86 backend (-fno-llvm -fno-lld). This is a way better debugging experience if you are using that backend.