fix(2meet-data-optimizer): close the gaps in deferred table upgrades found in the 2.3 review

- a deferred group whose stored definition matches again (reverted, or
  upgraded by another process) goes through end_deferral() instead of staying
  native for good (review F2)
- the tmdo_ensure_group_indexes handler upgrades deferred tables itself: with
  ALTERNATE_WP_CRON the event runs after init in a visitor's request (F3)
- a new group table created while the entity writes to flat stays native
  until the drift fix has filled it from native meta; an opted-in HivePress
  attribute no longer routes searches to an empty table (F6)
- direct_read() returns native values for a deferred group (F10); the Hook
  Bus ignores deferral in aeav_only, as the router does
- dbDelta failures: the definition is recorded only when every column exists
  (schema.upgrade_failed otherwise), so a failed ALTER is retried and the
  group is not released onto missing columns
- test bootstrap: get_metadata() reads the real meta table
- Verify: SchemaUpgradeDeferralTest (6), Hook Bus direct read, integration
  587, unit 703, phpcs, stan
- PR: PR-114 (2.3 acceptance correctness review)

tests/integration/bootstrap.php

@@ -299,6 +299,19 @@ if ( ! function_exists( 'do_action_ref_array' ) ) {
 if ( ! function_exists( 'is_admin' ) )       { function is_admin(): bool { return ! empty( $GLOBALS['_wp_is_admin'] ); } }
 if ( ! function_exists( 'is_singular' ) )    { function is_singular( $t = '' ): bool { return false; } }
 if ( ! function_exists( 'wp_doing_ajax' ) )  { function wp_doing_ajax(): bool { return false; } }
+if ( ! function_exists( 'get_metadata' ) ) {
+	// Like get_metadata(): the first stored value of a key (single), read from the real meta table.
+	function get_metadata( string $type, $object_id, string $key = '', bool $single = false ) {
+		global $wpdb;
+		$table = $wpdb->{$type . 'meta'};
+		$id    = 'user' === $type ? 'umeta_id' : 'meta_id';
+		$value = $wpdb->get_var( $wpdb->prepare( "SELECT meta_value FROM `{$table}` WHERE `{$type}_id` = %d AND meta_key = %s ORDER BY `{$id}` LIMIT 1", $object_id, $key ) );
+		if ( $single ) {
+			return null === $value ? '' : maybe_unserialize( $value );
+		}
+		return null === $value ? array() : array( maybe_unserialize( $value ) );
+	}
+}
 if ( ! function_exists( 'wp_next_scheduled' ) ) { function wp_next_scheduled( string $hook ): int|false { return false; } }
 if ( ! function_exists( 'wp_schedule_event' ) ) { function wp_schedule_event( int $t, string $r, string $h ): bool { return true; } }
 if ( ! function_exists( 'wp_schedule_single_event' ) ) { function wp_schedule_single_event( int $ts, string $hook ): bool { $GLOBALS['_wp_scheduled_single'][] = $hook; return true; } }