Attempt to be more performant on PyPy (#3462)

changelog.d/3462.feature

synapse/api/errors.py

synapse/api/filtering.py

synapse/crypto/keyclient.py

synapse/federation/federation_server.py

synapse/handlers/auth.py

synapse/handlers/e2e_keys.py

synapse/handlers/identity.py

synapse/handlers/message.py

synapse/http/client.py

synapse/http/matrixfederationclient.py

synapse/http/server.py

synapse/http/servlet.py

synapse/metrics/__init__.py

synapse/replication/tcp/commands.py

synapse/rest/client/v1/login.py

synapse/rest/client/v1/room.py

synapse/rest/client/v2_alpha/sync.py

synapse/rest/media/v0/content_repository.py

synapse/rest/media/v1/preview_url_resource.py