rewrite:

- rely on itlib::ref_ptr for unique() stability
- better naming
- unify Detached and OptDetached as ref_ptr
- optimize shared state

- No more zero-dep. Using CPM.cmake

- Using itlib types
- C++20 compat Improved shared_handle

- Redesigned pubsub. No more polymorphic subscriber.

- Renamed Root to State
- Allow shared detachable state
- ALIAS CMake target kuzco::kuzco
- Compact copyright notice in sources
- Latest CPM and dependencies

- By-handle subs

- Removed obsolete func

Separate header for Detached objects

Improved the interface of vector types

- Node vectors

- Attachable nodes
- Leaf typedefs
- CPM for tests

Modular headers

Initial release. Core types