When keying custom properties that are defined by an addon,
you can't use square brackets. The GUI buttons already reflect that.
The baking code and the keyframe insertion code didn't respect
that and so were able to key properties that are defined as non-keyable.
## Solutions
I've solved the issue on the C++ side by resolving
the path twice, once without and in case that didn't work the
second time with brackets. While that does solve the issue
this feels really dirty and I feel like I am misusing the system here.
**However it is absolutely needed**.
When resolving a path with brackets to a property defined
by an addon, you get an `IDProperty` disguised as a `PropertyRNA`
which will not have the correct flags set.
By checking if a property `is_animatable` in python, all that do not have that can be skipped.
Also making sure the path is passed without brackets in the correct cases.
Pull Request: https://projects.blender.org/blender/blender/pulls/121520
eee32726c7