* custom move ctor/op for the registry class
* no registry argument from storage emplace, remove, ...
* added sparse set context to forward variables to mixins
* removed sparse set user data
* sparse_set: added optional user data to ::remove and ::clear
* sparse_set: remove the payload, it was really meh
* storage: review sigh_storage_mixin, simplified storage_adapter_mixin
* registry: pass itself twhen adding/patchin/removing components
test: updated tests for sparse set and poly storage
examples: added a test to avoid regressions on storage_adapter_mixin
