Setting caching (#3178)

* Revert "Remove stat context variables"

This reverts commit 0989c308d0.

* Add a caching framework for inventree settings

- Actions that use "settings" require a DB hit every time
- For example the part.full_name() method looks at the PART_NAME_FORMAT setting
- This means 1 DB hit for every part which is serialized!!

* Fixes for DebugToolbar integration

- Requires different INTERNAL_IPS when running behind docker
- Some issues with TEMPLATES framework

* Revert "Revert "Remove stat context variables""

This reverts commit 52e6359265.

* Add unit tests for settings caching

* Update existing unit tests to handle cache framework

* Fix for unit test

* Re-enable cache for default part values

* Clear cache for further unit tests

InvenTree/part/test_part.py

@@ -3,6 +3,7 @@
 import os
 
 from django.conf import settings
+from django.core.cache import cache
 from django.core.exceptions import ValidationError
 from django.test import TestCase
 
@@ -394,6 +395,9 @@ class PartSettingsTest(InvenTreeTestCase):
 
     def make_part(self):
         """Helper function to create a simple part."""
+
+        cache.clear()
+
         part = Part.objects.create(
             name='Test Part',
             description='I am but a humble test part',
@@ -404,6 +408,9 @@ class PartSettingsTest(InvenTreeTestCase):
 
     def test_defaults(self):
         """Test that the default values for the part settings are correct."""
+
+        cache.clear()
+
         self.assertTrue(part.settings.part_component_default())
         self.assertTrue(part.settings.part_purchaseable_default())
         self.assertFalse(part.settings.part_salable_default())
@@ -411,6 +418,9 @@ class PartSettingsTest(InvenTreeTestCase):
 
     def test_initial(self):
         """Test the 'initial' default values (no default values have been set)"""
+
+        cache.clear()
+
         part = self.make_part()
 
         self.assertTrue(part.component)