[Feature Request] Measure request dispatch accuracy

[markVaykhansky]

Description
When using constant or poisson rates we would like to know how accurate the dispatch of requests really is.
So for each request we would like to have scheduled_time and actual sent_time as well as part of a summarized report file.

For example, if we have a constant rate of 1 RPS it would be meaningful to know that a request was sent after 1.2 seconds instead of 1 second.

Motivation
When analyzing the benchmarks in order to make decision regarding production grade workloads we need to know how accurate the measurement was. If the data is very skewed it would be wrong to make decisions based on it. Such problems are expected to arise under high load which makes it even more crucial to investigate as this is where systems typically fail.

[markurtz]

Closing this out now that #96 has landed on main. Each request stored in the output now contains a "scheduler_info" object which contains the request times here along with any other important times for the benchmarking process.