test: fill remaining V1 test coverage

Add JSONB, pointer/filter, MustFetchOne, and dialect logger registration
tests for dbxm and dbxp.

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

jsonb_test.go

@@ -0,0 +1,52 @@
+package dbx
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestJSONB_ScanValue(t *testing.T) {
+	original := JSONB{"key": "value", "num": float64(1)}
+
+	val, err := original.Value()
+	require.NoError(t, err)
+
+	var scanned JSONB
+	require.NoError(t, scanned.Scan(val))
+	assert.Equal(t, original["key"], scanned["key"])
+
+	require.NoError(t, scanned.Scan([]byte(`{"a":1}`)))
+	assert.Equal(t, float64(1), scanned["a"])
+
+	require.NoError(t, scanned.Scan(`{"b":2}`))
+	assert.Equal(t, float64(2), scanned["b"])
+}
+
+func TestJSONB_ScanNil(t *testing.T) {
+	j := JSONB{"x": 1}
+	require.NoError(t, j.Scan(nil))
+	assert.Nil(t, j)
+
+	val, err := JSONB(nil).Value()
+	require.NoError(t, err)
+	assert.Nil(t, val)
+}
+
+func TestJSONB_ScanUnsupportedType(t *testing.T) {
+	var j JSONB
+	err := j.Scan(123)
+	assert.Error(t, err)
+}
+
+func TestNewJSONB(t *testing.T) {
+	data := map[string]any{"k": "v"}
+	j := NewJSONB(data)
+	assert.Equal(t, JSONB(data), j)
+}
+
+func TestJSONB_String(t *testing.T) {
+	j := JSONB{"a": "b"}
+	assert.JSONEq(t, `{"a":"b"}`, j.String())
+}