Refactor network logs instrumentation for session replay

[marandaneto]

Description

Relates to PostHog/posthog-js-lite#276
#203 is a quick fix but instrumentation should be reworked so we instrument the datatask methods without a completion handler but we are still able to collect the right duration.
There are a few ways (and more complex) of doing this, such as instrumenting the delegate methods, wrapping the completion handlers, instrumenting the URLProtocol for complete control, etc.
My idea is to borrow the logic if possible from https://github.com/kasketis/netfox.
They do this in all possible ways and its a well known lib