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>

query_test.go

@@ -78,3 +78,16 @@ func TestFetchOne_NilWhenEmpty(t *testing.T) {
 	require.NoError(t, err)
 	assert.Nil(t, result)
 }
+
+func TestMustFetchOne_NotFound(t *testing.T) {
+	errNotFound := errors.New("not found")
+	stmt := mockStatement{
+		queryContextFn: func(_ context.Context, _ any) error {
+			return ErrNoRows
+		},
+	}
+
+	result, err := MustFetchOne[row](mockQueryable{}, stmt, errNotFound)
+	assert.Nil(t, result)
+	assert.ErrorIs(t, err, errNotFound)
+}