Add stub for doll-master and doll services, add required vendored libs

vendor/github.com/carlmjohnson/requests/serializer.go

@@ -0,0 +1,24 @@
+package requests
+
+import (
+	"encoding/json"
+)
+
+// Serializer is a function
+// that can convert arbitrary data
+// to bytes in some format.
+type Serializer = func(v any) ([]byte, error)
+
+// Deserializer is a function
+// that can read data in some format
+// and store the result in v.
+type Deserializer = func(data []byte, v any) error
+
+var (
+	// JSONSerializer is used by BodyJSON and Builder.BodyJSON.
+	// The default serializer may be changed in a future version of requests.
+	JSONSerializer Serializer = json.Marshal
+	// JSONDeserializer is used by ToJSON and Builder.ToJSON.
+	// The default deserializer may be changed in a future version of requests.
+	JSONDeserializer Deserializer = json.Unmarshal
+)