Generalize costs

[bentaculum]

• Generalizes the signature of costs Split and Appear to the weight, attribute, constant format of other costs. This now optionally allows for variable costs for these events.
• Adds an optional constant the EdgeDistance cost. Here the signature is positional_attributes, weight, constant, since positional_attributes is a compulsory argument.
• Updates the API test to cover these changes.

[codecov[bot]]

Codecov Report

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

Comparison is base (56469ee) 92.91% compared to head (1722dab) 93.37%. Report is 6 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #54 +/- ## ========================================== + Coverage 92.91% 93.37% +0.46% ========================================== Files 32 32 Lines 762 770 +8 ========================================== + Hits 708 719 +11 + Misses 54 51 -3 ```

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[funkey]

Thanks a lot for that! This looks good to me, with the exception of constant for EdgeDistance. This can already by done through EdgeSelection and would be redundant.

[bentaculum]

Good point. I removed this redundancy and updated the test accordingly.

[bentaculum]

Hi @funkey, ok to merge this?

[funkey]

Sorry for the delay. Yes, looks good, thanks a lot! :)