Performance improvements and refactor of Ratelimiter (#7595)

While working on https://github.com/matrix-org/synapse/issues/5665 I found myself digging into the `Ratelimiter` class and seeing that it was both:

* Rather undocumented, and
* causing a *lot* of config checks

This PR attempts to refactor and comment the `Ratelimiter` class, as well as encourage config file accesses to only be done at instantiation. 

Best to be reviewed commit-by-commit.

1 files changed, 2 insertions, 7 deletions

diff --git a/tests/rest/client/v1/test_rooms.py b/tests/rest/client/v1/test_rooms.py

index 7dd86d0c27..4886bbb401 100644
--- a/tests/rest/client/v1/test_rooms.py
+++ b/tests/rest/client/v1/test_rooms.py
@@ -20,7 +20,7 @@
 
 import json
 
-from mock import Mock, NonCallableMock
+from mock import Mock
 from six.moves.urllib import parse as urlparse
 
 from twisted.internet import defer
@@ -46,13 +46,8 @@ class RoomBase(unittest.HomeserverTestCase):
     def make_homeserver(self, reactor, clock):
 
         self.hs = self.setup_test_homeserver(
-            "red",
-            http_client=None,
-            federation_client=Mock(),
-            ratelimiter=NonCallableMock(spec_set=["can_do_action"]),
+            "red", http_client=None, federation_client=Mock(),
         )
-        self.ratelimiter = self.hs.get_ratelimiter()
-        self.ratelimiter.can_do_action.return_value = (True, 0)
 
         self.hs.get_federation_handler = Mock(return_value=Mock())