Fix tach report with Python files outside source roots; parallelize
#1517
| Job | Run time |
|---|---|
| 1m 32s | |
| 1m 43s | |
| 3m 11s | |
| 1m 23s | |
| 1m 32s | |
| 1m 50s | |
| 1m 44s | |
| 12m 55s |