Check updated_at timestamp on lists

[craigjmidwinter]

Describe the problem
I've got some big personal trakt lists that I follow that only update sporadically, but they get polled every time traktarr runs even though they haven't changed and all the items already exist in radarr.

Describe any solutions you think might work
Lists seem to provide an updated_at timestamp that could be stored so that only one page of results need to be requested per list