Bug 33102: Display fields from biblioitems in OPAC/staff interface cart

The OPAC/PRO cart only displays biblio fields coming from 'biblio'
table. Fields from biblioitems table aren't displayed anymore.

TO TEST:

1. Populate a cart in OPAC/staff interface and display it.
2. You can see that Year column is empty (if you don't have copyright
   field). And other fields.
3. Apply the patch.
4. You can see more fields in cart simple/detailed view.

Signed-off-by: Magnus Enger <magnus@libriotech.no>
Tested by having a record with:
- biblio.copyrightdate = NULL
- biblioitems.publicationyear = 2025
Without the patch, no year is shown in the cart. With the patch, 2025 is shown.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 2056b5ecec)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

basket/basket.pl

@@ -64,7 +64,7 @@ foreach my $biblionumber ( @bibs ) {
     $template->param( biblionumber => $biblionumber );
 
     my $biblio           = Koha::Biblios->find( $biblionumber ) or next;
-    my $dat              = $biblio->unblessed;
+    my $dat              = { %{$biblio->unblessed}, %{$biblio->biblioitem->unblessed} };
     my $record           = $biblio->metadata->record;
     my $marcnotesarray   = $biblio->get_marc_notes;
     my $marcauthorsarray = $biblio->get_marc_contributors;

opac/opac-basket.pl

@@ -71,7 +71,7 @@ foreach my $biblionumber ( @bibs ) {
     $template->param( biblionumber => $biblionumber );
 
     my $biblio           = Koha::Biblios->find( $biblionumber ) or next;
-    my $dat              = $biblio->unblessed;
+    my $dat = { %{$biblio->unblessed}, %{$biblio->biblioitem->unblessed} };
 
     # No filtering on the item records needed for the record itself
     # since the only reason item information is grabbed is because of branchcodes.