.resolver.resolve_user should return the username/service with the User namedtuple

[erkghlerngm44]

Something to add in, if it doesn't slow down the function substantially (over many runs).

Though there's not really much point? The code using it wouldn't need to be changed, and I'm not sure if the function would even be used outside of this package and the soulmate finder...

[erkghlerngm44]

As tuple:

>>> import timeit
>>> timeit.timeit('aniffinity.resolver.resolve_user("XXX", "ANILIST")', setup="import aniffinity")
0.6346462229999972

As namedtuple:

>>> import timeit
>>> timeit.timeit('aniffinity.resolver.resolve_user("XXX", "ANILIST")', setup="import aniffinity")
1.5054766589999993

On average, 8.7E^-7 slower (0.87 secs slower overall)

So shouldn't make that much of a difference.