refactor: peerRequestQueue

	it's a mistake to make one queue to fit all. Go's lack of algebraic
	types turns a generalized queue into a monstrosity of type
	checking/casting. Better to have individual queues for individual
	purposes.

	Conflicts:
		exchange/bitswap/decision/bench_test.go
		exchange/bitswap/decision/tasks/task_queue.go

	fix(bitswap.decision.PRQ): if peers match, always return result of pri comparison

	fix(bitswap.decision.Engine): push to the queue before notifying

	TOCTOU bug

	1. client notifies
	2. worker checks (finds nil)
	3. worker sleeps
	3. client pushes (worker missed the update)

	test(PQ): improve documentation and add test

	test(bitswap.decision.Engine): handling received messages

	License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>