Benchmark of ThreadTimer, System.currentTimeMillis() and System.nanoTime()

Benchmark code
```
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Measurement(iterations = 5, time = 30)
@Fork(1)
@State(Scope.Benchmark)
public class BenchmarkTimer {

public static void main(String[] args)
throws Exception {
ChainedOptionsBuilder opt = new OptionsBuilder().include(BenchmarkTimer.class.getSimpleName());
new Runner(opt.build()).run();
}

@Benchmark
public void benchmarkThreadCpuTimer() {
ThreadTimer threadTimer = new ThreadTimer();
long totalThreadCpuTimeNs = threadTimer.getThreadTimeNs();
}

@Benchmark
public void benchmarkSystemCurrentTimeMillis() {
long startWallClockTimeMs = System.currentTimeMillis();
long totalWallClockTimeMs = System.currentTimeMillis() - startWallClockTimeMs;
long totalWallClockTimeNs = TimeUnit.MILLISECONDS.toNanos(totalWallClockTimeMs);
}

@Benchmark
public void benchmarkSystemNanoTime() {
long startWallClockTimeNs = System.nanoTime();
long totalWallClockTimeNs = System.nanoTime() - startWallClockTimeNs;
}
}

```

Benchmark result of adoptopenjdk-11.jdk on macOS Monterey v12.0.1
```
Benchmark Mode Cnt Score Error Units
BenchmarkTimer.benchmarkSystemCurrentTimeMillis avgt 5 54.111 ± 12.025 ns/op
BenchmarkTimer.benchmarkSystemNanoTime avgt 5 61.704 ± 0.645 ns/op
BenchmarkTimer.benchmarkThreadCpuTimer avgt 5 0.526 ± 0.023 ns/op
```

Benchmark result of jdk11.0.10-msft.jdk on macOs Big sur v11.6.1
```
Benchmark Mode Cnt Score Error Units
BenchmarkTimer.benchmarkSystemCurrentTimeMillis avgt 5 48.704 ± 2.548 ns/op
BenchmarkTimer.benchmarkSystemNanoTime avgt 5 56.387 ± 2.091 ns/op
BenchmarkTimer.benchmarkThreadCpuTimer avgt 5 0.476 ± 0.009 ns/op
```

Looks like thread cpu time measuring (retrieve from java.lang.management.ThreadMXBean) has little overhead, while wall clock time measuring (need a system call. Depends on the JVM and OS, the system call can be accelerate by vDSO to avoid user-space/kernel-space switch) is much more expensive.

cc @siddharthteotia @richardstartin

The issue provides standalone BenchmarkTimer methods comparing ThreadTimer, System.currentTimeMillis(), and System.nanoTime(), but names no repository file or test. First clarify whether a benchmark should be added and where it belongs; completion would require an agreed benchmark location, reproducible measurements, and documented comparison results.

Written by the indexing model from the issue text.