Unify `RequestList` and `RequestProvider` interfaces and extract their "tandem" behavior from `BasicCrawler`

[janbuchar]

Initial steps have been taken in #2498.

• [ ] Introduce a IRequestProvider interface
• [ ] Unify IRequestProvider with IRequestList
• [ ] Introduce a "switching" request provider implementation to better encapsulate the logic of "read from list first, add new requests to queue" currently present in BasicCrawler
• [ ] The transfer from request list to request queue should be done in background, not when fetching requests from the queue

[janbuchar]

Python implementation here https://github.com/apify/crawlee-python/pull/777