Expected benchmark with usl4j

[Ale142]

This PR introduces the ExpectedBenchmark class which allows creating a scaling model based on the us4lj library and the Universal Scalability Law.

Update of loadtest script

Commit efec4ef modifies index.js script (loadtest): previously (ba51d2a) there was a for loop on the number of concurrent clients but I noticed that this implementation created an incorrect calculations of the rps, request per seconds.

Now the for loop has been removed and the script can be launched in the CLI by specify the number of concurrent clients with the option -c or --clients

node index.js -c [num]

[fxbrit]

after running:

for i in 1 2 4 8 16 32                 
do
    node index.js -c $i
done

I got:

concurrency,totalRequest,totalErrors,totalTimeSeconds,rps,meanLatencyMs,maxLatencyMs,minLatencyMs

1,10000,10000,77.21972838800001, 130,7.7,13112,0
2,10000,10000,79.741377486, 125,15.6,25913,0
4,10000,10000,97.61991096999999, 102,39,13115,0
8,10000,10000,82.593626027, 121,66,13116,0
16,10000,10000,106.099865032, 94,169.7,13130,1
32,10000,10000,89.459510421, 112,280.4,25930,1

---

the main branch instead produced:

concurrency,totalRequest,totalErrors,totalTimeSeconds,rps,meanLatencyMs,maxLatencyMs,minLatencyMs

32,10000,10000,176.50398286700002, 57,542.1,25939,0
16,10000,10000,208.033274442, 48,331.7,25932,0
8,10000,10000,322.307709304, 31,257.8,25932,1
4,10000,10000,406.645655809, 25,162.6,25930,0
2,10000,10000,468.879125346, 21,93.4,25931,0
1,10000,10000,519.568257536, 19,51.9,25931,0

[Ale142]

There is also a lot of difference in your case between the new version and the on in main branch. I would say we can merge now. Thanks a lot