[wperf-scripts] Add to regression tests sleep between core loads

For some tests, when we spawn new process with wperf stat ... [PROCESS] [ARGS] and wperf record ... [PROCESS] [ARGS] we would like to make sure that when new test is executed core(s) are not yet counting previous micro-benchmark process.

This patch adds simple time.sleep calls to all tests executing above commands.

Regression tests

>pytest
================================== test session starts ===================================
platform win32 -- Python 3.11.1, pytest-7.2.0, pluggy-1.0.0
rootdir: C:\Users\$USER\Desktop\wperf\merge-request\386, configfile: pytest.ini
collected 153 items / 1 skipped

wperf_cli_common_test.py ....                                                       [  2%]
wperf_cli_config_test.py .....                                                      [  5%]
wperf_cli_extra_events_test.py ....                                                 [  8%]
wperf_cli_info_str_test.py .                                                        [  9%]
wperf_cli_json_validator_test.py ........                                           [ 14%]
wperf_cli_list_test.py .....                                                        [ 17%]
wperf_cli_metrics_test.py ................                                          [ 28%]
wperf_cli_padding_test.py ...........                                               [ 35%]
wperf_cli_record_test.py ..............                                             [ 44%]
wperf_cli_stat_test.py ...................................................          [ 77%]
wperf_cli_test_test.py .....                                                        [ 81%]
wperf_cli_timeline_test.py ....................                                     [ 94%]
wperf_cli_ustress_bench_test.py ......                                              [ 98%]
wperf_cli_ustress_dep_record_test.py .                                              [ 98%]
wperf_cli_ustress_dep_wperf_test.py .                                               [ 99%]
wperf_lib_app_test.py s                                                             [100%]

================================ short test summary info =================================
SKIPPED [1] wperf_cli_ustress_dep_wperf_lib_timeline_test.py:110: Can not find wperf-lib-timeline.exe
SKIPPED [1] wperf_lib_app_test.py:44: Can not run wperf-lib-app.exe
======================= 152 passed, 2 skipped in 258.08s (0:04:18) =======================