proto: Add helper function to marshal Message

It will be useful for `interface { Marshal() []byte }` implementations.

Signed-off-by: Leonard Lyubich <[email protected]>

internal/proto/encoding.go

@@ -21,6 +21,13 @@ type Message interface {
 	MarshalStable(b []byte)
 }
 
+// MarshalMessage returns m encoded to dynamically allocated buffer.
+func MarshalMessage(m Message) []byte {
+	b := make([]byte, m.MarshaledSize())
+	m.MarshalStable(b)
+	return b
+}
+
 // Bytes is a type parameter constraint for any byte arrays.
 type Bytes interface{ ~[]byte | ~string }