Improve readability and interpretability of code by explicitly stating null in union types. This
change has been applied across multiple files and functions.

PHP8.4 compatibility

Added a conditional check in src/QUI/ERP/Order/Basket/Basket.php to convert basketId to actual id
from user's session if it is a boolean value. This fixes potential issues that may arise with
non-integer basketIds.

Also, introduced a safeguard check before saving to ensure there is a valid User. If not, the save
function is exited early to prevent potential errors or undesired actions.

Related: order-guestorder#6

Related: order-guestorder#6

For orders this is not needed. the internal instance cache causes more problems
due to the mix between uuid and id cache. the internal cache on uuid / id was therefore removed.
Orders have the data freshly fetched from the db anyway. therefore unnecessary.
In addition, a wrong order object was repeatedly retrieved when sending mail.

Related: quiqqer/order#163

Orders have not taken over the customer id.

Related: pcsg/buero#453

The UX was not optimal as a result. It was not clear that you could scroll and the guest order button was not visible.
For now flex removed and the login buttons are below each other

Related: template-cologne#111

fix: only prevent writing of invoice_id in order if order already has a (non-temporary) invoice assigned

related: quiqqer/order-guestorder#8

(cherry picked from commit 065225a2)

Co-authored-by: Michael Danielczok <michael@pcsg.de>

Added global process id click, too

related: pcsg/buero#432