Make secondary arguments of `models` optional

[adtzlr]

also make everything in /src flake8 compliant

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (8cae7d9) 100.00% compared to head (8d8f993) 100.00%.

:exclamation: Current head 8d8f993 differs from pull request most recent head b504fa7. Consider uploading reports for the commit b504fa7 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #131 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 24 24 Lines 986 994 +8 ========================================= + Hits 986 994 +8 ``` | [Impacted Files](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler) | Coverage Δ | | |---|---|---| | [src/matadi/\_lab\_incompressible.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9fbGFiX2luY29tcHJlc3NpYmxlLnB5) | `100.00% <ø> (ø)` | | | [src/matadi/models/\_hyperelasticity\_anisotropic.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9tb2RlbHMvX2h5cGVyZWxhc3RpY2l0eV9hbmlzb3Ryb3BpYy5weQ==) | `100.00% <ø> (ø)` | | | [src/matadi/\_\_about\_\_.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9fX2Fib3V0X18ucHk=) | `100.00% <100.00%> (ø)` | | | [src/matadi/\_\_init\_\_.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9fX2luaXRfXy5weQ==) | `100.00% <100.00%> (ø)` | | | [src/matadi/\_material.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9fbWF0ZXJpYWwucHk=) | `100.00% <100.00%> (ø)` | | | [src/matadi/\_templates.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9fdGVtcGxhdGVzLnB5) | `100.00% <100.00%> (ø)` | | | [src/matadi/math.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9tYXRoLnB5) | `100.00% <100.00%> (ø)` | | | [src/matadi/models/\_\_init\_\_.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9tb2RlbHMvX19pbml0X18ucHk=) | `100.00% <100.00%> (ø)` | | | [src/matadi/models/\_helpers.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9tb2RlbHMvX2hlbHBlcnMucHk=) | `100.00% <100.00%> (ø)` | | | [src/matadi/models/\_hyperelasticity\_isotropic.py](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL21hdGFkaS9tb2RlbHMvX2h5cGVyZWxhc3RpY2l0eV9pc290cm9waWMucHk=) | `100.00% <100.00%> (ø)` | | | ... and [5 more](https://codecov.io/gh/adtzlr/matadi/pull/131?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler) | |

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