fix(2meet-data-optimizer): compare empty strings correctly when retiring a group

- retire() read native meta with wpdb::get_col(), which (via get_var())
  returns null for an empty string, so a flat '' written back as '' was
  counted as a mismatch and blocked the retirement. It now reads raw rows
  with get_results().
- The integration test wpdb stub's get_var() / get_col() now read '' as
  null like the real wpdb, so tests see WordPress behaviour.
- Found writing back the sso group on dev21 / dev22 (picture_url = '').
- Verify: core unit 658 / integration 480 green, phpcs clean
- PR: PR-042 follow-up

tests/integration/NativeRestorerRetireTest.php

@@ -129,6 +129,15 @@ class NativeRestorerRetireTest extends TestCase {
 		$this->assertSame( 3, $result['mismatches'], 't1, ["1.1.1.1"], t2 are not native yet' );
 	}
 
+	public function test_empty_string_values_count_as_written_back(): void {
+		global $wpdb;
+		$wpdb->query( 'UPDATE `' . self::A . "` SET ips = '' WHERE user_id = 2" );
+		TMDO_Native_Restorer::run( 'user', false, 500, false, 'rt_a' );
+		self::register( false );
+
+		$this->assertSame( 'retired', TMDO_Native_Restorer::retire( 'user', 'rt_a' )['status'], "wpdb::get_col() reads '' as null" );
+	}
+
 	public function test_retire_forgets_the_group_and_keeps_its_table_as_a_backup(): void {
 		global $wpdb;
 		TMDO_Native_Restorer::run( 'user', false, 500, false, 'rt_a' );