All Submissions:

• Have you followed the WooCommerce Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Note that this PR targets cot/meta_migrations and not trunk. In case #32640 is merged earlier, target for this PR would need to be updated to trunk.

Partially closes #32663. Handles migration part of that change. DB schema will be handled as part of separate PR.

How to test the changes in this Pull Request:

1. Make sure that you have {prefix}_wc_orders, {prefix}_wc_order_addresses, {prefix}_wc_order_operational_data and {prefix}_wc_orders_meta table created by following steps from Add DB table structure for custom order tables. #31811.
2. Run migration using the following snippet:

namespace Automattic\WooCommerce\Database\Migrations\CustomOrderTable;
$done = false;
$migrator = new WPPostToCOTMigrator();
delete_option( 'wc_cot_migration' );
$start_time = microtime( true );
while( ! $done ) {
	$batch_start = microtime( true );
	$done = $migrator->process_next_migration_batch( 500 );
	echo 'Batch completed in ' . ( microtime( true ) - $batch_start ) . ' seconds' . "\n";
}
$duration = microtime( true ) - $start_time;
echo $duration;

4. Make sure that migrated order records have the same ID as their corresponding posts id.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?
• Have you created a changelog file by running pnpm nx affected --target=changelog?

FOR PR REVIEWER ONLY:

• I have reviewed that everything is sanitized/escaped appropriately for any SQL or XSS injection possibilities. I made sure Linting is not ignored or disabled.