sotw code cleanup

[alecholmez]

• moves server unit tests to assert
• removes code duplication inside of the watches

[alecholmez]

@snowp I ported the logic over from delta to sotw so we cleanup the existing code a bit 😄 .

In another PR we can address the following bugs: #431 #399

But just wanted to get us in a place where those will be easy to implement

[snowp]

There is a slight perf concern (additional goroutines per stream) with making this change, I wonder if we want to wait until we have mem/speed benchmarks until we make a change like this to SotW since it's in active use?

[alecholmez]

@snowp I'm not opposed to that. go routines are relatively lightweight but I think it's a good idea to measure the current performance first.