feat: add StringKSUID and BinaryKSUID types

Replace the UUID wrapper with storage-specific KSUID types that share
GraphQL string transit but use distinct SQL Scan/Value encodings.

Co-authored-by: Cursor <cursoragent@cursor.com>

ksuid_gql.go

@@ -0,0 +1,37 @@
+package dbx
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+
+	"github.com/segmentio/ksuid"
+)
+
+type ksuidGQLTransport struct {
+	KSUIDStr string `json:"ksuid_str"`
+}
+
+func unmarshalKSUIDFromGQL(value any, unmarshal func([]byte) error) error {
+	str, ok := value.(string)
+	if !ok {
+		return fmt.Errorf("GraphQL failed to unmarshal KSUID value: %v", value)
+	}
+	return unmarshal([]byte(str))
+}
+
+func marshalKSUIDToGQL(w io.Writer, id ksuid.KSUID) {
+	transport := ksuidGQLTransport{KSUIDStr: id.String()}
+	data, err := json.Marshal(transport)
+	if err != nil {
+		panic(fmt.Errorf("GraphQL failed to JSON-marshal KSUID value: %s", err))
+	}
+	if _, err := w.Write(data); err != nil {
+		panic(fmt.Errorf("GraphQL failed to write KSUID value: %s", string(data)))
+	}
+}
+
+const (
+	ksuidBinaryLength = 20
+	ksuidStringLength = 27
+)