new: emit after event

[DonutEspresso]

I thought this was going to be straight forward but it got messy much more quickly than I expected. This mostly had to do with a patchwork of how the request lifecycle was being handled. In short, this PR:

• Changes base HttpClient to always "end" a request lifecycle using a unified emitResult() function call (It used to call req.emit('result') in various places)
• Adds an onResult() handler in StringClient to listen to the result event, using that handler to then invoke parse() to parse the response body
• Upon successful parsing of the response body, the user land provided callback is invoked, along with the the after event.
• This PR also attaches the recently added metrics object on to the request via req.getMetrics() method

Because HttpClient consumes the streams directly, after doesn't really seem to make sense there. Thus, it's implemented in only StringClient and JSONClient. The tests aren't anywhere close to being complete - but wanted to get a sanity check first from the peanut gallery.

[DonutEspresso]

I also want to add that the implementations of the parse() method leave a bit to be desired - it mixes the lower level http errors along with parsing errors, and is quite difficult to reason about. I think it's worth addressing at some point but a bit outside of the scope of this PR, so I've kept the logic mostly intact.

[DonutEspresso]

Finished adding the complete suite of tests.

[DonutEspresso]

Thanks all, I tried to address all comments with the latest commits. Just to be sure, are we all aligned on HttpClient not emitting the after event? I think it makes sense to me but want to make sure I'm not missing anything.

[DonutEspresso]

Summarizing some offline conversations:

We'll support after even on the HttpClient, but errors cannot be as fully fleshed out as JSONClient/StringClient since the HttpClient does not do any response parsing. It's on userland to augment the existing error. If new errors are created in the callback (e.g., parsing errors), the only way after can get access to them is if it's tacked on via the request or response objects.

[DonutEspresso]

This PR is now ready for a final pass.

[misterdjules]

@DonutEspresso Latest changes look good to me! Thank you! 🙏

[DonutEspresso]

Thanks for the feedback all!