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>

dbxm/mysql_test.go

@@ -0,0 +1,15 @@
+package dbxm_test
+
+import (
+	"testing"
+
+	"gitea.auvem.com/go-toolkit/dbx"
+	"gitea.auvem.com/go-toolkit/dbx/internal/dbxshared"
+	_ "gitea.auvem.com/go-toolkit/dbx/dbxm"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMySQLDebugLoggerRegistered(t *testing.T) {
+	err := dbxshared.InitLogger(dbx.DialectMySQL)
+	assert.NoError(t, err)
+}