SwiftNetwork: PERF: Optimize Serializer

[agnosticdev]

This is a first pass at optimizing Serializer Operations. This largely applies the same optimizations made to the deserializer here #82 and optimizes UInt64+VLE operations as well.
We see roughly a ~50% decrease in CPU usage here:

// Top of tree
2.03 G 100.0%	-	Serializer.serialize

// With this change
1.05 G 100.0%	-	Serializer.serialize

I have another pass I am going to do, but its a much larger scope.