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• Allow configuring concurrent request response status #4 by @laurynas
• Fix Ruby 2.7 Warnings #5 by @douglaslise

• use ActiveSupport::Notifications to instrument events
• fix an issue when getting an exception inside application would not delete lock, so client could receive 429 after 500

Fix an issue, when http response from backend != 200..226 caused lock to be taken

Fix an issue, when concurrent requests sent to an endpoint won't be protected by idempotency until the 1st request is finished

• Fix rack response
• Disuse SETNX (@espadrine)

Cache all the successful responses (200..226)