make utils.py work with cached queryset results dict

[anufry]

This will protect from DB query for each currency filter usage (1 query per hour, until model would not be changed)

[asucrews]

@panosl, @anufry, i going to pull these changes in my fork and see if they work with Django 4.

If it does I open a new PR, this seems like a really good feature to add.