Add max_threads_per_process and mp_context to pca by channel computation and PCA metrics
#1302
| Job | Run time |
|---|---|
| 7m 8s | |
| 13m 15s | |
| 8m 10s | |
| 7m 20s | |
| 14m 20s | |
| 9m 43s | |
| 59m 56s |