Optimise PC regression

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.61905% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 59.00%. Comparing base (9c5a936) to head (344fb75).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #408 +/- ## ========================================== + Coverage 54.60% 59.00% +4.39% ========================================== Files 22 22 Lines 1683 1705 +22 ========================================== + Hits 919 1006 +87 + Misses 764 699 -65 ``` | [Flag](https://app.codecov.io/gh/theislab/scib/pull/408/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/theislab/scib/pull/408/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab) | `59.00% <97.61%> (+4.39%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/theislab/scib/pull/408?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab) | Coverage Δ | | |---|---|---| | [scib/metrics/cell\_cycle.py](https://app.codecov.io/gh/theislab/scib/pull/408?src=pr&el=tree&filepath=scib%2Fmetrics%2Fcell_cycle.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab#diff-c2NpYi9tZXRyaWNzL2NlbGxfY3ljbGUucHk=) | `89.58% <100.00%> (+0.22%)` | :arrow_up: | | [scib/preprocessing.py](https://app.codecov.io/gh/theislab/scib/pull/408?src=pr&el=tree&filepath=scib%2Fpreprocessing.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab#diff-c2NpYi9wcmVwcm9jZXNzaW5nLnB5) | `18.95% <100.00%> (ø)` | | | [scib/metrics/pcr.py](https://app.codecov.io/gh/theislab/scib/pull/408?src=pr&el=tree&filepath=scib%2Fmetrics%2Fpcr.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab#diff-c2NpYi9tZXRyaWNzL3Bjci5weQ==) | `91.11% <97.05%> (+9.95%)` | :arrow_up: | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/theislab/scib/pull/408/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab)