Change Packets To Structs

[liamdalg]

Current Behaviour: the packets are lots of small classes, which will be allocated on the heap, and lead to bad GC.

Desired Behaviour: switch to structs so we use the stack more often. We also might be able to take advantage of the stackalloc keyword with arrays maybe? https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/stackalloc

[ghost]

@ChrisGora has coronavirus