Add filters

[richardjgowers]

Just need to add some tests for these...

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +1.03 :tada:

Comparison is base (9b87908) 91.27% compared to head (7c25e6b) 92.30%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #9 +/- ## ========================================== + Coverage 91.27% 92.30% +1.03% ========================================== Files 4 7 +3 Lines 424 481 +57 ========================================== + Hits 387 444 +57 Misses 37 37 ``` | [Impacted Files](https://app.codecov.io/gh/OpenFreeEnergy/kartograf/pull/9?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy) | Coverage Δ | | |---|---|---| | [src/kartograf/\_\_init\_\_.py](https://app.codecov.io/gh/OpenFreeEnergy/kartograf/pull/9?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy#diff-c3JjL2thcnRvZ3JhZi9fX2luaXRfXy5weQ==) | `100.00% <100.00%> (ø)` | | | [src/kartograf/atom\_mapper.py](https://app.codecov.io/gh/OpenFreeEnergy/kartograf/pull/9?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy#diff-c3JjL2thcnRvZ3JhZi9hdG9tX21hcHBlci5weQ==) | `87.12% <100.00%> (-0.48%)` | :arrow_down: | | [src/kartograf/filters/\_\_init\_\_.py](https://app.codecov.io/gh/OpenFreeEnergy/kartograf/pull/9?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy#diff-c3JjL2thcnRvZ3JhZi9maWx0ZXJzL19faW5pdF9fLnB5) | `100.00% <100.00%> (ø)` | | | [src/kartograf/filters/element\_change.py](https://app.codecov.io/gh/OpenFreeEnergy/kartograf/pull/9?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy#diff-c3JjL2thcnRvZ3JhZi9maWx0ZXJzL2VsZW1lbnRfY2hhbmdlLnB5) | `100.00% <100.00%> (ø)` | | | [src/kartograf/filters/ring\_changes.py](https://app.codecov.io/gh/OpenFreeEnergy/kartograf/pull/9?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy#diff-c3JjL2thcnRvZ3JhZi9maWx0ZXJzL3JpbmdfY2hhbmdlcy5weQ==) | `100.00% <100.00%> (ø)` | |

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[RiesBen]

looks very cool so far :)