refactor: Sandbox for separation of boundaries

sandbox/platform/platform_unsupported.go

@@ -0,0 +1,15 @@
+//go:build !darwin && !linux && !windows
+// +build !darwin,!linux,!windows
+
+package platform
+
+import (
+	"errors"
+
+	"github.com/safedep/pmg/sandbox"
+)
+
+// NewSandbox returns an error on unsupported platforms.
+func NewSandbox() (sandbox.Sandbox, error) {
+	return nil, errors.New("sandbox not supported on this platform")
+}