feat: add method for setting env vars

crates/runix/src/command_line/mod.rs

@@ -231,6 +231,14 @@ impl NixCommandLine {
 
         M::run(&mut command).await
     }
+
+    // Set the global Nix config via the environment variables in flox.default_args so that
+    // subprocesses called by `flox` (e.g. `parser-util`) can inherit them.
+    pub fn export_config_env_vars(&self) {
+        for (name, value) in self.defaults.environment.iter() {
+            std::env::set_var(name, value);
+        }
+    }
 }
 
 /// Create a list of arguments from `&Self`