Newznab capability

[blades]

I've added a plugin using the same architecture as the prowlarr plugin to enable Newznab as a source.
I've tested locally with nzbhydra2 and it all seems to work as intended.
I've added some unit tests for this feature, and found that a couple of other unit tests weren't behaving so fixed those up while I was at it. I also ran all of the linters in the makefile against it and fixed those up, too, so hopefully this should be as clean and as compatible as it can be.

[alexhb1]

Hi, looks great. Works well for me.

You've caught me at a slightly awkward time, there's been a ton of lint + quality + test changes these last couple days so things might be a little out of date. Could you rebase with just /release-sources/newznab and /tests/newznab/ additions included and make sure it's still passing with the new checks? Then should be good to go, thanks :)

[blades]

Sure thing - this should now be updated. Nice to see the additional linting in the makefile as well - probably the most comprehensive suite I've seen, tbh.
Thanks - glad it's a useful addition :)