better GAM, better random forest in readme

[mayer79]

• The GAM has now an interaction, and cool plots
• The random forest was too bad due to short trees. Now, no tree.depth is set.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (060d4eb) 96.40% compared to head (b70df39) 96.40%.

:exclamation: Current head b70df39 differs from pull request most recent head 6eae1c3. Consider uploading reports for the commit 6eae1c3 to get more accurate results

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #125 +/- ## ======================================= Coverage 96.40% 96.40% ======================================= Files 6 6 Lines 473 473 ======================================= Hits 456 456 Misses 17 17 ```

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