Move require outside of benchmark method for fairness

```
# Running benchmarks:

Process information retrieval	1	10	100	1000	10000
bench_POSIX_Spawn_popen4	 0.002088	 0.001913	 0.001926	 0.001812	 0.001770
bench_Process_stats	 0.000034	 0.000037	 0.000036	 0.000031	 0.000028
bench_Process_stats_children	 0.000041	 0.000033	 0.000033	 0.000037	 0.000035
bench_Process_stats_self	 0.000046	 0.000040	 0.000035	 0.000034	 0.000036
bench_Spawn_ps_rss	 0.009240	 0.008660	 0.012322	 0.010561	 0.007450
bench_System_uname	 0.000038	 0.000018	 0.000012	 0.000011	 0.000011
Finished benchmarks in 0.273769s, 21.9163 tests/s, 21.9163 assertions/s.
6 tests, 6 assertions, 0 failures, 0 errors, 0 skips
```