Updates for one shipment per oder

[a-zagroba]

Body:

Summary

• Single-shipment-per-order mode now uses the merchant's default parcel
  dimensions/weight from settings instead of summing every item's
  dimensions (which produced unrealistic shipment sizes).
• Extended PayseraDeliverySettingsInterface with
  getDefaultParcelWidth/Height/Length/Weight().
• ShipmentsAdapter::convert() now takes the full
  PayseraDeliverySettingsInterface instead of a bool flag, so it can
  read both the toggle and the default parcel size from one source.
• Bumped to 0.5.0 and updated CHANGELOG.md.

Changes

• src/Adapter/ShipmentsAdapter.php — createSingleShipment() reads
  defaults from settings; signature of convert() updated.
• src/Adapter/OrderCreateRequestAdapter.php,
  src/Adapter/OrderUpdateRequestAdapter.php — pass DeliverySettings
  to ShipmentsAdapter::convert().
• src/Entity/PayseraDeliverySettingsInterface.php — 4 new getters.
• tests/Adapter/ShipmentsAdapterTest.php — updated to new signature
  and asserts the parcel uses the defaults from settings.

Breaking changes

ShipmentsAdapter::convert() signature changed from
(OrderItemsCollection, bool) to
(OrderItemsCollection, PayseraDeliverySettingsInterface).
Any implementer of PayseraDeliverySettingsInterface must add the four
new getDefaultParcel*() methods.

Test plan

• composer test (PHPUnit) passes
• PHPStan / CS-Fixer clean
• Manual: order placed with single-shipment toggle ON produces one
  shipment with the merchant's default parcel dimensions
• Manual: toggle OFF still creates one shipment per item

[gemini-code-assist]

Code Review

This pull request updates the shipment creation logic to use merchant-defined default parcel dimensions for single-shipment orders instead of summing individual item dimensions. Key changes include updates to the ShipmentsAdapter, the PayseraDeliverySettingsInterface, and the corresponding request adapters. Feedback from the review suggests adding a check to prevent creating shipments for empty orders in single-shipment mode and improving PHPDoc documentation for better static analysis.