more readable PCA computation and info retrieval

[codecov[bot]]

Codecov Report

Merging #377 (2c172eb) into main (48c5e93) will decrease coverage by 0.08%. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #377 +/- ## ========================================== - Coverage 53.34% 53.26% -0.08% ========================================== Files 22 22 Lines 1854 1851 -3 ========================================== - Hits 989 986 -3 Misses 865 865 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `53.26% <100.00%> (-0.08%)` | :arrow_down: | 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. | [Impacted Files](https://codecov.io/gh/theislab/scib/pull/377?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab) | Coverage Δ | | |---|---|---| | [scib/\_package\_tools.py](https://codecov.io/gh/theislab/scib/pull/377?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab#diff-c2NpYi9fcGFja2FnZV90b29scy5weQ==) | `86.66% <ø> (ø)` | | | [scib/metrics/lisi.py](https://codecov.io/gh/theislab/scib/pull/377?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab#diff-c2NpYi9tZXRyaWNzL2xpc2kucHk=) | `42.13% <100.00%> (ø)` | | | [scib/metrics/pcr.py](https://codecov.io/gh/theislab/scib/pull/377?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=theislab#diff-c2NpYi9tZXRyaWNzL3Bjci5weQ==) | `81.15% <100.00%> (-0.79%)` | :arrow_down: |