Merge pull request #1030 from matrix-org/erikj/cache_contexts

synapse/push/action_generator.py

synapse/push/bulk_push_rule_evaluator.py

synapse/storage/_base.py

synapse/storage/event_push_actions.py

synapse/storage/push_rule.py

synapse/storage/pusher.py

synapse/storage/receipts.py

synapse/storage/signatures.py

synapse/storage/state.py

synapse/util/caches/descriptors.py

synapse/util/caches/lrucache.py

synapse/util/caches/treecache.py

tests/storage/test__base.py

tests/util/test_lrucache.py