[FIX] prefetch issues on computed/related fields

When deciding to prefetch records (getting records from the cache with
no value for the field being fetched), if the field was computed
determine_value would just get all records, not limited by the normal
prefetch limit, for large recordsets this would generate gigantic
prefetch lists for records we may not need at all.

Fix by applying the PREFETCH_MAX limit to records from the cache as is
done in _prefetch_field.

Complementarily, when traversing related fields the prefetch
environment would be lost and every record would get an empty prefetch
environment, so the values would ultimately be read one by one.

Example: select (search) 1000 product.product records, access a
related field (e.g. categ_id) in a loop, on the first iteration the
system would first read 1000 templates, then it would read each
categ_id individually, resulting in >1000 SQL queries rather than the
~2 we would expect.

Fixes odoo#18511

odoo/fields.py

@@ -568,7 +568,7 @@ def traverse_related(self, record):
         """ Traverse the fields of the related field `self` except for the last
         one, and return it as a pair `(last_record, last_field)`. """
         for name in self.related[:-1]:
-            record = record[name][:1]
+            record = record[name][:1].with_prefetch(record._prefetch)
         return record, self.related_field
 
     def _compute_related(self, records):
@@ -981,6 +981,8 @@ def determine_value(self, record):
                 self.compute_value(record)
             else:
                 recs = record._in_cache_without(self)
+                if len(recs) > PREFETCH_MAX:
+                    recs = recs[:PREFETCH_MAX] | record
                 self.compute_value(recs)
 
         else:
@@ -2445,4 +2447,4 @@ def __set__(self, record, value):
 # imported here to avoid dependency cycle issues
 from odoo import SUPERUSER_ID
 from .exceptions import AccessError, MissingError, UserError
-from .models import check_pg_name, BaseModel, IdType
+from .models import check_pg_name, BaseModel, IdType, PREFETCH_MAX