Integrate go-varsig and go-did-it

- go-varsig provides a varsig V1 implementation
- go-did-it provides a complete and extensible DID implementation

pkg/args/builder_test.go

@@ -6,6 +6,7 @@ import (
 	"github.com/ipld/go-ipld-prime"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
 	"github.com/ucan-wg/go-ucan/pkg/args"
 )