Refactor `EventContext` (#12689)

Refactor how the `EventContext` class works, with the intention of reducing the amount of state we fetch from the DB during event processing.

The idea here is to get rid of the cached `current_state_ids` and `prev_state_ids` that live in the `EventContext`, and instead defer straight to the database (and its caching). 

One change that may have a noticeable effect is that we now no longer prefill the `get_current_state_ids` cache on a state change. However, that query is relatively light, since its just a case of reading a table from the DB (unlike fetching state at an event which is more heavyweight). For deployments with workers this cache isn't even used.


Part of #12684

1 files changed, 3 insertions, 1 deletions

diff --git a/tests/test_visibility.py b/tests/test_visibility.py

index d0230f9ebb..7a9b01ef9d 100644
--- a/tests/test_visibility.py
+++ b/tests/test_visibility.py
@@ -234,7 +234,9 @@ class FilterEventsForServerTestCase(unittest.HomeserverTestCase):
         event = self.get_success(builder.build(prev_event_ids=[], auth_event_ids=[]))
         event.internal_metadata.outlier = True
         self.get_success(
-            self.storage.persistence.persist_event(event, EventContext.for_outlier())
+            self.storage.persistence.persist_event(
+                event, EventContext.for_outlier(self.storage)
+            )
         )
         return event