Refactor: Use niquests rather requests

[glensc]

• support for requests-cache
• support for requests-oauthlib

[glensc]

Seems both requests packages that we use have usage documented:

• https://niquests.readthedocs.io/en/latest/community/recommended.html#requests-cache
• https://niquests.readthedocs.io/en/latest/community/recommended.html#requests-oauthlib

[glensc]

Some odd lockup happens:

• from debug log i see shows are fetched from trakt that are not even in progressbar

i.e progressbar is stuck on first item on first library, but logs show it's processing items from next library.
and oddly the episodes it fetches are not cached, always 200, so likely requests cache doesn't get complete response yet to store to cache. likely awaiting for one single item, but which one? the traceback is not helpful as it just tons of corotines...