Remove transport abstraction and use separate controllers

[kalabukdima]

Removed the abstract Transport in favor of separate HttpController and P2PController. They both own a reference to the Worker that handles query execution and downloads. It also allowed to unify HTTP interface for both scenarios. However, in the P2P case the /query endpoint will always return NoAllocation error to avoid free execution.

What still needs to be done:

• Consider moving allocations checking to the controller. Right now, the P2PController always uses Worker with RpcAllocationsChecker and HttpController uses Worker with NoopAllocationsChecker.
• All the background tasks are now just join-ed instead of halting the execution as soon as one of the tasks finishes. I want to integrate this logic into the TaskManager and get it back after that.

[Wiezzel]

@kalabukdima StateManager::run() is never called, so the worker doesn't download anything. 😢