Make elapsed time available in the `response` event hook

[joaonc]

There are two types of elapsed time on a response:

• The current .elapsed that accounts for total time of request, including event hooks. This is what we have now (Related to Make .elapsed reflect the entire response time. #655).
• The elapsed time of the actual request, not taking into account the event hooks, which can take a significant amount of time, depending on what you're doing. This number is currently not available.

In many scenarios, we have request and/or response event hooks that do a time consuming process, but need the time of the actual request only, w/o event hooks. Prime example is logging the response in a response event hook and we want to include the elapsed time in the response.

Is it possible to add a mechanism in which:

• We can access the elapsed time w/o the time to process event hooks.
• Have that time available in the response hook.