Extract handlers independent frommiddleware-mockserver.cjs into a separatemiddleware-handlers.js file; add a separate wrapper for working with the nginx JavaScript engine.

I wanted to get some opinions on whether this makes sense. nginx can be used with njs or QuickJS; I used the latter as njs is very limited (it doesn't even support named imports). JS feature support is pretty good but most Node.js modules are missing. On the other hand, handlers returning the status code, headers & body don't need a lot beyond the ability to read files (which works) & read the full body (available out of the box). I'm also readingimport.meta.dirname which is not supported either so I'm just passing the dirname from nginx.

Right now the nginx version only fails the multipart form data test, I haven't migrated that part. The rest passes.

A caveat: the nginx version available on macOS via Homebrew doesn't include the js module and it's impossible to add one. There's a separate tap for full nginx butit's broken at the moment.

I tried using the Dockernginx:alpine image and it worked without major issues, though. I could even use the config I currently use on macOS with only minor changes to enable the JS engine. The command to set this up:

docker run -d \  --name nginx-njs \  -p 80:80 \  -v /Users/mgol/projects/public/jquery/jquery-core:/Users/mgol/projects/public/jquery/jquery-core \  -v /Users/mgol/www/vhosts:/Users/mgol/www/vhosts \  -v /opt/homebrew/etc/nginx:/opt/homebrew/etc/nginx:ro \  -v /opt/homebrew/var/log/nginx:/opt/homebrew/var/log/nginx \  nginx:alpine

Then I just had to drop the/etc/nginx folder and create a symlink to/opt/homebrew/etc/nginx in its place and add some config to the js module. It shouldn't be hard to create a Dockerfile for this if we wanted to make it easier for others as well.

If we were to land this, I'd prefer to do this in multiple PRs to not lose history onmiddleware-mockserver.cjs.