option to enable allowUnfree = true for non-flake-based nix setups.
Not sure if this limited to only non-flake-based setups, but that's what I'm using when I observed the following.
I'm managing nix on macos with nix-darwin and managing user-level settings with home-manager. I have allowUnfree = true in my home-manager definition, which then pipes that argument to ~/.config/nixpkgs/config.nix. I'm not using flakes presently. Since mise-nix is using nix build, it doesn't see my user-level config. Adding --impure flag to nix build command in vsix.lua does enable the ability for mise-nix to evaluate my config.nix containing the allowUnfree = true.
Or perhaps as an alternative to adding --impure flag, mise-nix could be configured to enable allowUnfree = true as the default.
I will add flags for this in the next version. Also for insecure. thanx for reporting