* Print key in map.getitem/delitem KeyError
* Add tests
* Fix tests
* Make robust
* Make clang-tidy happy
* Return a Python str
* Show beginning and end of the message
* Avoid implicit conversion
* Split out `format_message_key_error_key_object()` to reduce amount of templated code.
* Use `"✄✄✄"` instead of `"..."`
Also rename variable to `cut_length`, to not get into even/odd issues with the meaning of "half".
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Co-authored-by: Ralf W. Grosse-Kunstleve <rgrossekunst@nvidia.com>
