Protect: improve performance of requests to the Protect API

### Impacted plugin

Protect

### What

Using website with Jetpack Protect is slow in US rush hours

### How

I was debugging a site that has been extremally slow during USA business hours. The site itself has not been receiving almost any traffic, server load was low etc.. In other hours, it has been working okay.


XDebug has traced this to be caused by curl HTTP requests by Jetpack and Astra. Disabling Jetpack and the offending features of Astra helped.

It seems that these days, it's possible to use [asynchronous execution for HTTP](https://stackoverflow.com/questions/962915/how-do-i-make-an-asynchronous-get-request-in-php/13545561#13545561) - even in PHP. Would you consider using this to not slow down your users' websites when your server gets slow?

Start by identifying the Jetpack Protect curl HTTP requests described in the report and profiling their effect when the Protect API is slow during US business hours. Compare the current synchronous behavior with the proposed asynchronous approach; done should mean slow Protect API responses no longer make users' websites slow. The issue names no files or tests.

Written by the indexing model from the issue text.