refactor( for less complexity when reading)

[Ipuch]

This change is 

[codeclimate[bot]]

Code Climate has analyzed commit e423b9cb and detected 0 issues on this pull request.

View more on Code Climate.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 82.41758% with 16 lines in your changes are missing coverage. Please review.

Project coverage is 83.51%. Comparing base (ce64f52) to head (e423b9c). Report is 1 commits behind head on main.

Files	Patch %	Lines
bionc/bionc_casadi/natural_inertial_parameters.py	74.07%	7 Missing :warning:
bionc/bionc_numpy/natural_inertial_parameters.py	80.76%	5 Missing :warning:
bionc/bionc_casadi/natural_coordinates.py	83.33%	2 Missing :warning:
bionc/bionc_numpy/natural_coordinates.py	81.81%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #135 +/- ## ========================================== + Coverage 83.36% 83.51% +0.14% ========================================== Files 91 91 Lines 5862 5842 -20 ========================================== - Hits 4887 4879 -8 + Misses 975 963 -12 ``` | [Flag](https://app.codecov.io/gh/Ipuch/bioNC/pull/135/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+Puchaud) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/Ipuch/bioNC/pull/135/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+Puchaud) | `83.51% <82.41%> (+0.14%)` | :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=Pierre+Puchaud#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.