build: add determinate nix support for darwin

- Add determinateSystems/determinate flake input
- Include determinate darwin modules in configuration
- Disable legacy nix module configuration
- Remove modules/darwin/nix/default.nix
- Add mac-va-mbp-work system using determinate nix

modules/darwin/default.nix

@@ -1,5 +1,6 @@
 {
   config = {
+    nix.enable = false;
     home-manager = {
       useGlobalPkgs = true;
       useUserPackages = true;