feat(graphql): add JS-safe uint64 marshal helpers

Adds MarshalUint64, UnmarshalUint64, and Uint64Marshaler for gqlgen-
compatible uint64 string scalars without a gqlgen dependency.

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

gql_uint64_test.go

@@ -0,0 +1,49 @@
+package dbx
+
+import (
+	"bytes"
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMarshalUint64(t *testing.T) {
+	var buf bytes.Buffer
+	MarshalUint64(9007199254740993).MarshalGQL(&buf)
+	assert.Equal(t, `"9007199254740993"`, buf.String())
+}
+
+func TestUnmarshalUint64_String(t *testing.T) {
+	n, err := UnmarshalUint64("42")
+	require.NoError(t, err)
+	assert.Equal(t, uint64(42), n)
+}
+
+func TestUnmarshalUint64_Number(t *testing.T) {
+	n, err := UnmarshalUint64(float64(42))
+	require.NoError(t, err)
+	assert.Equal(t, uint64(42), n)
+}
+
+func TestUnmarshalUint64_RoundTripJSON(t *testing.T) {
+	const original uint64 = 9007199254740993
+	var buf bytes.Buffer
+	MarshalUint64(original).MarshalGQL(&buf)
+
+	var wire string
+	require.NoError(t, json.Unmarshal(buf.Bytes(), &wire))
+
+	got, err := UnmarshalUint64(wire)
+	require.NoError(t, err)
+	assert.Equal(t, original, got)
+}
+
+func TestUnmarshalUint64_Invalid(t *testing.T) {
+	_, err := UnmarshalUint64(true)
+	assert.Error(t, err)
+
+	_, err = UnmarshalUint64(float64(-1))
+	assert.Error(t, err)
+}