Fix Risk Index calculation and add data sanitization

[yihuicai]

1. The length of chunk_BG should be 20 to calculate ri_per_hour, since the gap between two records is 3 mins.
2. The last element of chunk_BG may not be full. This will affect the accuracy of the ri_mean.
3. np.mean() is no longer compatible (see Risk index calculation error in report generation #61 ) Use similar caculation in risk.py

[jxx123]

@yihuicai Would you mind adding a test for report.py? I know the code in report.py is really crappy, so it would be nice to have a test for it. Thank you for fixing the compatibility issue BTW! Really appreciate it.

[yihuicai]

@yihuicai Would you mind adding a test for report.py? I know the code in report.py is really crappy, so it would be nice to have a test for it. Thank you for fixing the compatibility issue BTW! Really appreciate it.

Sure, just added a test for risk index report.

[jxx123]

Thank you for adding the unit test! I will approve this change after you fix the minor naming and parameter default issues. Thanks again!

[jxx123]

Thank you. LGTM.

[yihuicai]

Seems the workflow didn't pass the test I wrote but did pass locally for me. I changed the accuracy of float number results. Let's see if it works.