Refactor of trytond.config to add cache

This removes the need to store configuration in global variable and so make it
easier to update for example for testing.

Closes #14249

modules/timesheet_cost/company.py

@@ -2,8 +2,8 @@
 # this repository contains the full copyright notices and license terms.
 from decimal import Decimal
 
+import trytond.config as config
 from trytond.cache import Cache
-from trytond.config import config
 from trytond.model import Index, ModelSQL, ModelView, Unique, fields
 from trytond.pool import Pool, PoolMeta
 from trytond.transaction import Transaction