* use slices.BinarySearchFunc with its boolean status
* use slices.Insert/slices.Delete, tnis can be a little less efficient, but it
frees the memory faster and this code is more I/O (networking) bound to care
about 1-3%
Signed-off-by: Roman Khimov <roman@nspcc.ru>
We need to copy the result of `TryGet` method, otherwice the slice can
be modified inside `Add` or `Update` methods, which leads to
inconsistent MPT pool state.
In this commit:
1. Request unknown MPT nodes from peers. Note, that StateSync module itself
shouldn't be responsible for nodes requests, that's a server duty.
2. Do not request the same node twice, check if it is in storage
already. If so, then the only thing remaining is to update refcounter.
