remove mutex lock in a goroutine lifecycle

[HyungrakJo]

There is a performance loss due to mutex locks in situations where goroutines are frequently created/exited.

1. I used lock free pool as goroutine id pool.
2. In order to get the "Values" corresponding to the goroutine id, I made it possible to access without contention by using a pre-assigned array instead of map. It is assumed that the array can grow variably and holds write locks only when it needs to be grown.

It was confirmed that there is a significant performance difference by modifying the benchmark test case.

• before

BenchmarkGetValue-10    	    2514	    551195 ns/op
BenchmarkSetValues-10    	    6830	    166487 ns/op

• after

BenchmarkGetValue-10    	    4240	    505839 ns/op
BenchmarkSetValues-10    	   15340	     76396 ns/op