1.6.1 Fix legacy WooCommerce order correlation without HPOS

[DaanRijpkema]

Summary

• preserve Bluem custom order query arguments when WooCommerce HPOS is disabled
• keep the HPOS metadata mapping active only for the HPOS order datastore
• add regression coverage for legacy order storage
• align plugin, readme, and translation metadata with version 1.6.1

Cause

The HPOS query adapter was registered for all WooCommerce order queries. With classic order storage it removed the custom mandate or payment correlation argument before the legacy CPT datastore filter could translate it. The resulting query was unfiltered and returned the newest order, causing mandate callbacks to update the wrong order.

Verification

• PHP 8.4 syntax checks passed
• Composer validation and platform requirements passed
• CI PHPUnit suite: 56 tests, 151 assertions
• production package compared byte-for-byte with live 1.6.0 except for the intended fix and version metadata
• WordPress.org release 1.6.1 published as SVN revision 3669413

Release scope

This branch starts from the exact Git source matching WordPress.org trunk 1.6.0 so later unreleased master changes are not included.