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/replication/slave/storage/_base.py b/tests/replication/slave/storage/_base.py

index 32cb04645f..56497b8476 100644
--- a/tests/replication/slave/storage/_base.py
+++ b/tests/replication/slave/storage/_base.py
@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from mock import Mock, NonCallableMock
+from mock import Mock
 
 from tests.replication._base import BaseStreamTestCase
 
@@ -21,12 +21,7 @@ from tests.replication._base import BaseStreamTestCase
 class BaseSlavedStoreTestCase(BaseStreamTestCase):
     def make_homeserver(self, reactor, clock):
 
-        hs = self.setup_test_homeserver(
-            federation_client=Mock(),
-            ratelimiter=NonCallableMock(spec_set=["can_do_action"]),
-        )
-
-        hs.get_ratelimiter().can_do_action.return_value = (True, 0)
+        hs = self.setup_test_homeserver(federation_client=Mock())
 
         return hs