Ensure System.Runtime.GetNotifications can't break MaxStackSize constraint

[AnnaShaleva]

This test ensures that NeoGo node doesn't have the DeepCopy problem described in neo-project/neo#3300 and fixed in neo-project/neo#3301. This problem leads to the fact that Notifications items are not being properly refcounted by C# node which leads to possibility to build an enormously large object on stack. Go node doesn't have this problem.

The reason (at least, as I understand it) is in the fact that C# node performs objects refcounting inside the DeepCopy even if the object itself is not yet on stack. I.e. System.Runtime.Notify handler immediately adds references to the notification argumetns inside DeepCopy:
https://github.com/neo-project/neo/blob/b1d27f0189861167b8005a7e40e6d8500fb48cc4/src/Neo.VM/Types/Array.cs#L108
https://github.com/neo-project/neo/blob/b1d27f0189861167b8005a7e40e6d8500fb48cc4/src/Neo.VM/Types/Array.cs#L75

Whereas Go node just performs the honest DeepCopy without references counting:

neo-go/pkg/vm/stackitem/item.go

Line 1223 in b66cea5

arr.value[i] = deepCopy(it.value[i], seen, asImmutable)

Going further, C# node clears refs for notification arguments (for array and underlying array items). Sytem.Runtime.GetNotifications pushes the notificaiton args array back on stack and increments counter only for the external array, not for its arguments. Which results in negative refcounter once notificaiton is removed from the stack. The fix itself (https://github.com/Jim8y/neo/blob/f471c0542ddd8f527478fbdcda76a3ab9194b958/src/Neo/SmartContract/NotifyEventArgs.cs#L84) doesn't need to be ported to NeoGo because Go node adds object to the refcounter only at the moment when it's being pushed to stack by System.Runtime.GetNotifications handler. This object is treated as new object since it was deepcopied earlier by System.Runtime.Notify handler:

neo-go/pkg/vm/stack.go

Line 178 in b66cea5

s.refs.Add(e.value)

.

Thus, no functional changes from the NeoGo side. And we won't intentionally break our node to follow C# pre-Domovoi invalid behaviour.

Close #3484, close #3482.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 86.10%. Comparing base (b66cea5) to head (effba1f).

❗ Current head effba1f differs from pull request most recent head d156cea

Please upload reports for the commit d156cea to get more accurate results.

Files	Patch %	Lines
pkg/vm/stackitem/item.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3485      +/-   ##
==========================================
- Coverage   86.13%   86.10%   -0.04%     
==========================================
  Files         331      331              
  Lines       38482    38487       +5     
==========================================
- Hits        33146    33138       -8     
- Misses       3805     3818      +13     
  Partials     1531     1531              

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