Investigate System.Runtime.Notify refcounting

[AnnaShaleva]

Need to investigate how stackitem refcounting works for System.Runtime.Notify handler for both Go and C# nodes.

[AnnaShaleva]

For the record: I investigated NeoGo code and turns out that Notifications size is not restricted in any way. I also deployed a contract and tried to send a lot of notifications, so it's confirmed in practice that it's possible for NeoGo.

However, for C# node there's a chance that notifications number is restricted. The restriction goes from the way how C# VM refcounting works (hi, #2500), and if emitted Notifications are refcounted properly in C#, then the behaviour of C# and Go nodes is different. But for now I can't tell for sure what is the behaviour of C# node, we need to check it on practice using the same contract as for Go node and check the resulting behaviour (but not in mainnet/testnet, please).

[AnnaShaleva]

OK, I can't find the branch, but the contract was based on TestEngineLimits.